The Writhing Wall communal event is certainly an interesting idea and, ignoring for a moment that it dragged on too long, I would say it's overall part of the experience when you're playing this year's content. However, it can't stay around forever and that's only natural but that is also going to cause issues that I don't believe ZOS has sufficiently prepared for. We won't really know for sure until after the event is complete so know that a lot of this is going to be speculation, but I will try to go over this very thoroughly. Naturally, there will be story spoilers!

The way things stand right now, everything is going well when it comes to the Seasons of the Worm Cult story-line... but only for players that are caught up on the story! This begs the question: "How is this going to work for new players that weren't around for the event?". It's probably safe to assume that it would be best for the story to replicate the experience of the event as closely as possible (though improvements aren't out of the question). This story-line relies a lot on the Writhing Wall. There's a slow build up: First, you learn to understand what the Wall is, then you determine how to overcome it, you lay siege to it, you weaken it, you break through, you destroy it's power source and then, and only then, can the Wall come down. The limitations brought on by the Wall also define the story and if any of these things are left out or subverted, the entire story ceases to make sense! So, whatever content ZOS plans to substitute in for the event has to obey a number of conditions that I'm going to outline now:

1. No player character must be allowed to enter Eastern Solstice under any circumstances until after they have achieved the necessary story milestones! (whether or not it was wise to set it up this way is another matter but story consistency demands it!)
2. There has to be a real passage of time between the 5th main quest and the crossing of the wall in order to explain the significant increase in Stirk Fellowship fighters, the building of siege camps, and the construction and charging of the Meridian Lens.
3. And lastly, the power source of the Wall has to be made accessible to the player. Something as significant as the Writhing Fortress is too integral to the story to be skipped over without at least a suitable substitute!

Point 1 should be self-explanatory. If there were any option to get past the wall without first restoring the Light of Merida, the entire Western Solstice story line would lack all foundation.

Point 2 would be trickier. Obviously, the whole experience and the amount of progress needed would need to be re-balanced and scaled down to what a single player could achieve in a reasonable amount of time but in order to figure out what exactly they ought to do there, we first need to understand what we've been doing this past month.
Gathering Resources, making equipment... We've basically taken on the role of NPCs and as such the crafting and supply quests could probably be removed without repercussions to the story. It just needs to be clearly communicated that theses efforts are taking place if just behind the scenes now.
What definitely has to stay are the Siege Camps and the corresponding quest, and resolving a set amount of these ought to be part of the progress requirement.
As for the Lens Charging quest... it's hard to figure out what to do with it. We could get rid of it in the same way as crafting and supply quest or leave it as is but I have some ideas for substitutes, too:

• Quests involving the invaded delves and public dungeons (which also weren't meant to stay around after the event). the affected location could be loaded into a solo or group instance, inaccessible to the general public. For example: "We have received intel about a Worm Cult nest at [invaded location]. They appear to have obtained "a store of vitrified souls"/"a powerful vitrified soul". root them out and retrieve the item"
• Quests that send you back to some of the story areas (and maybe new ones) under the writhing Wall to weaken it further.
• Quests that allow you to gain favor with the Three Queens (Meridia, Nocturnal, Azura) so they empower the Meridian Lens.

... just to name a few options. Any and all of these could be made available. In fact I would advise splitting the responsibility of this task among more than 1 quest giver, because you have to preserve the appearance that a lot of energy is needed to charge the Lens. These kind of daily quests would also be fine to keep around after the Wall is down, just like the Siege Camps. From a lore point of view, this kind of labor would continue to be useful to the Stirk Fellowship even without the Writhing Wall still around.
Then there's a question of how and in what form to preserve the phase structure of the activity. Increasing difficulty and concurrent encounters for the Siege Camps from phase 1 to phase 2 isn't going to be possible anymore, so we are probably going to need an indirect substitute. One thing that comes to mind is a variation upon the Lens Charging quests. I probably wasn't the only one who felt a bit strange in phase 1, charging a lens that didn't exist yet. So how about quests that are all about constructing the Meridian Lens instead! For example:

• A passive quest where you gather parts for the lens. Something comparable to the Museum Pieces from previous years or The Precursor from Clockwork City. something like the Vvardenfell model that gets filled in piece by piece would probably be ideal. possibly even with a starting quest (such as obtaining schematics) and a capstone quest (such as a final ritual)

Considering how little is required to build the Lens compared to how much is needed to fuel it, I think it's probably best whatever quest is put there in phase 1 is a one-time story quest rather than the daily quests of phase 2.

Finally, there is the matter of the Writhing Fortress...
I think most players will probably agree with me when I say that the Writhing Fortress would have been a huge waste of development time if it's really removed, never to be seen again after the event. Not just because, generally speaking, removing content from a game is pretty much the worst thing a developer can do to the player base, but also because the Fortress was easily the most enjoyable part of the event. Having been there once is probably not going to be enough. "What about the future players that won't get to see it?" "What about the next time I make a new character in order to play this story again?"... Let's just say it would be in everyone's best interest to keep the Writhing Fortress available. So let's discuss options.
The easiest thing would be to leave it in game as is and have it remain the final requirement to bring down the Wall and advance the story. But since it was designed as the centerpiece of an event, this may not be the best option. So what can we change or even improve about it to keep everything lore consistent and accessible?

• The Writhing Fortress is located in a planemelded area between Nirn and Coldharbour. it exists regardless of it's connection to the worm cult's energy source, which we cut off during the encounter. So there's nothing that speaks against revisiting the area after the Wall is down, which would be necessary to actually properly fill the instances with other players to make successful assault plausible.
• One thing that I found bothersome was that it was difficult to enter a fresh instance. missing out on encounters because the other players beat them before you entered wasn't much fun. So I would suggest making it a closed instance in the style of a Trial.
  • To that end, I would also recommend adding weekly quests. There could be one quest to prevent the Worm Cult from repairing the Soul Spire but side quests could be fun too. This should also help attract enough players. But they need to offer rewards that actually make it worth doing. Amongst other rewards, we need to make the title available again!
  • This shouldn't make it harder for people to get to Eastern Solstice, because taking down the Wall seems mostly cosmetic anyway since we put a hole into it. A hole whose existence can be justified by saying the lens weakened this spot enough to not only open to the planemelded area but also to the other side of the wall (though visual changes may be a good idea for that). However, in this case we may need to make some slight changes to the writing so that the requirement for advancing the main story is just breaching the wall and then taking it down would be an independent offshoot that can be done at any time.
• Considering the size of the Fortress and the way it is structured, namely the 4 distinct path that need to be completed (2 paths per wing), it seems clear that this is supposed to be a 24 player activity and should be properly balanced with this expectation.
• Because this activity is also designed in the style of a Public Dungeon, I think it may be possible to offer additional game modes intended for the lower player numbers. There would need to be balance and perhaps even some gameplay changes to accommodate this. I think even a mode for just 1 to 4 players could be an option if we supplement the narrative with and NPC army that accompanies you. where to put them and how to make them seem about as powerful as the players without causing problems would be a very important question to solve for this to work.

Beyond all these options listed above, I think we should also consider some general gameplay changes here and there. I think the East Wing is probably fine as is but perhaps something could be done about the West Wing. The siege weapons are thematically appropriate but operating and maintaining them could perhaps be handed over to NPCs and maybe players could then instead be tasked with defending them. It might also be nice to get more use out of the Infernium during the boss fight. But I'm not sure if that would be an improvement so it would need to be tested first. perhaps it's already enough to have the weapons last more than 2 hits and give the players that don't currently use them another task to do. Additional complexity of the boss fight might also be worth testing. As for the the Central Path to the finale, perhaps something more could be added to it so it doesn't feel like it's just the East Wing again.

Now I would just like to take a moment to encourage ZOS to actually make changes to the way they designed this zone if they find that it's not actually consistent enough after all.

Anyway these would be my thoughts on the matter. I hope I'm not the only one who feels this way because there's a lot of potential in this story line and it would be a shame to see it fall short like some of the previous year-long stories.