TESO offers a lot of great quests to do. However the actual roleplay comes short.
So my general idea for events would be replaying ingame quests RPG style. Like ending the siege on Viraak or defeating the brothers of strife etc. This way a group could gather and simply roleplay the quests through - with all the in character talking and action that you would normally do, like making a plan instead of just rushing in, getting wounded, scouting, travelling, sneaking in, taking out important targets silently and so on and so forth.
Since there are many quests i guess this can fill a looooot of events and all different kinds of tastes. Solving murder cases, fighting armies, gathering information, hunting down ferocious beasts...the game itself offers a lot there.
Some quests can be done even if you already did them, others are phased and may require either new characters or "imagining the enemies would still be there"