Wanna preface this by saying this is by no means a new problem and has existed for...a while now.

So I have ESO+ most of the time on my main, but sometimes it lapses and I don't have the moolah to drop on getting it for my alt account. It's not usually much of an issue, I can just send the mats from my alt to my main, though at some point I WILL need to set up a character as my crafter on that account. The main reason is I mostly need to be able to recon Gear on my alt, since reconned Gear is Bound. I also need to be able to reliably upgrade Bound Gear on that account, so while I don't need an all out Grand Master Crafter on that account, I need a crafter who can Do The Stuff™.

Now the problem that's existed for a while and is just getting worse with new mats (and yet more stuff like Sets) coming with U51. There have been NO actual inventory space upgrades since the game launched over a decade ago now. I don't count the Pets because they only give five slots per Pet and each once needs to be bought from the CS (afaik at least). That's not anywhere near a fraction of all the items that have been added since the game launched. I suppose one might say that the Craft Bag and Furnishing Vault are, in a way, upgrades, but at the same time not really. Both are locked to ESO+ and both only hold specific items. I'm talking character/bank space expansions.

The older the game gets, the worse this problem is going to keep getting. Yeah, we have eight characters default we can use as mules. And the first few bag upgrades on each aren't TOO expensive. However they do jump in price quite abruptly after the first handful, and while Mount Training is three times as fast these days, it's still a full month before you get that maxed. It's also a bit of a pain to do it on numerous characters every single day. HOWEVER. I am very much willing to bet most people who have multiple characters have a lot of different things those specific characters carry. Whether it's RP stuff, different sets for Trials/Dungeons, Potions and Food/Drink, things like Repair Kits and Siege for PvPers, or any other number of things, I feel like a majority of people might not have a bunch of slots to hold on to any number of other random things in their character inventories.

Yes, one could say "decon Gear you aren't using and just recon it later if you need it", that requires a decent stock of Transmutes and/or having farmed most or all of the Set so it's cheap to make. Also if you decon something you've reconned, you only get back 25 Transmutes even if that thing costed more to make and you only have a chance to get back some of the mats that went into it (like any improvement items). It can also be a pain since to recon things in any given Trait you need to have that Trait examined, so people who are working on their crafter might not really have this as a viable option, at least not for a while (and they might need that thing again before they have the chance to make it again). This is, admittedly, less of a problem now that Researching takes so much less time than it used to, but it COULD still be an issue.

And while inventory management is better in terms of Surveys, Maps, and Writs stacking the way they do now, that doesn't address people who don't have Plus who might be holding on to any number of important mats (like improvement items and rarer/valuable Alchemy ingredients for example) or any amount of Furniture. One could say "just stuff extra Furniture in a House" but the problem with THAT is we can't access Furniture to place if it's already in a House, aside from special things like Mounts and Busts obviously.

Having to store things on "mules" or in Houses makes things more complicated than it needs to be. At some point it feels like ZOS is going to need to expand expand bank/character inventory slots, or add things that AREN'T all locked behind ESO+. Maybe some sort of Armory (probably named something else so it wouldn't get confused with the Armory Station) that can hold Armor, Weapons, and Jewelry. Maybe add limited versions of the Craft Bag and Furniture Vault to base game, perhaps they can only hold 1/4 or 1/3 of what the paid versions do but can store at least enough to give people some breathing room. Maybe all of the above. But this is a problem that's just going to keep getting worse the older the game gets and more things are added to it.