Is there a mod which replaces the original npcs, quests, etc with OB lore-compatible content? I want to visit morrowind contemporary with the Emperor's death, not the Nerevarine - if i wanted that, i would just play morrowind.
If there isn't, is there anyone who will collaborate with me on such a mod?

You do know that morrowind
You do know that morrowind came before the emperors death in oblivion, and as such should be played before oblivion, right? Whats the point of making a mod that makes lore backwards compatible when you can just play the first part first? You see it is all oblivion lore compatible already. If morrowind is played first you hear about how Uriel septim VII rules the empire from cyrodil. Unless I'm not understanding you quite right, (Which, with me, is a great possibility.) I don't get why you would want to put together a mod like this.