imagine if you will, a singular large boss encounter, as if from a trial (but larger as its the whole point) limited to a singular instance, that singular instance is limited to a singular "arena" (think something a bit larger than a battleground arena.
for instance, say with a launch of summerset, there was some large beastie in a cavern, a new icon on the map, and an overworld effect noting the current state of the instance at a glance within the world (think like the anchors or geysers) you see nothing if it is dead, a slight glow of a beam in the air if it is about to spawn, and a dramatic light show effect if it is currenty summoned.
you proceed to the entrance to this dungeon, and enter the instance (the encounter is designed to require the teamwork of lets say 6 due to mechanics alone, 12 is solid, but the instance supports up to 24 individual players per instance) the party size is capped at 12
you enter and find a large open caver before you with a large creature roaming around the center, and several other players chilling in front of you near the entrance waiting for more people, maybe a full raid, a smaller group, and a couple solo players.
deciding you are ready, you engage with the fight, the raid group seems to know what its doing and you mostly just contribute to damaging the boss when possible, clearing adds as they spawn in, trying to figure out the mechanics as you watch others trigger events or deal with situations, you may even die but another one of the solo players seeing a buddy down runs over to revive you.
after about 15-20 (and perhaps a player leaving because of some real world reason, but quickly replaced by another player droping into the instance) minutes of fighting the boss finally goes down, chests spawn in the center of the chamber and your able to get yourself some decent loot. from here the event is over, but you know in another hour signs of this event will begin to appear, and you decide that your totally going to come back for more then, and perhaps group up with a few next time, imparting bits of the mechanics you were able to gleam on others and maybe try to figure it all out, and complete that set you want but only got the boots to . . .and motifs. . . and probably a skin.
that is my basic design of the overworld raid encounter and how it can be made accessible to many types of players who would otherwise not participate (or be able to) in classic dungeon or trial content. by making a large singular instanced encounter with drop in / out mechanics scaled around a base number required (min), a max group size (med), then a max instance size (max) I think the closest game examples I could actually point to would be eidolons in warframe or raid bosses in borderlands, as their singular encounters that can be solo'd or made easy with groups.
anyway, food for thought.
@ZOS_RichLambert
ESO player since beta.
game got too disappointing.