I think that we should develop quests that exist in game. I mean, you finsished quest for FG where you have to help Larienna Marcinia in Dwemer ruins and you ask hrundi about Larienna and he tells you that she is exploring Dwemer ruin near Blacklight. I think she should really be there.
The next person, Sondaale, an adventurer from Telasero should somewere in Mournholod because Hrundi says that she is looking for Sotha Sil town.
There was also man on Solstheim, that necromancer with a great robe(forify conjuration 100 pts), if you didn't kill him, he sholud be on Vvardenfell.
There are "dozens" of that NPCs in game and they should be use with that script like Fast Eddie(teleport?).
Sorry for my English, I hope you understand me, what you think about it?
You could have, near Dres, the Falen family asking you for news about their Drulene. You could find Duvianus Platorius on the continent, looking for Addhiranir after you told him she fled to the mainland. You could find Tashpi Ashibael in the Redoran lands if you let her flee... And so on...
I don't think it necissarily has to be a bolt on. Most of them would be just fine in game. All you have to do is a quick check to see if the quest that they last are on is finished and if it is you can enable the NPC on the mainland.
If you want to develop this, feel free to do it here. If people like it and it doesnt affect Vvardenfell then the moderators will probably allow it into the main mod anyway. But do try it, and keep us posted.
Fair enough, feel free to tinker any time you want, most of the exteriors are done so theres plenty of scope for sticking stuff in exteriors, and theres no need to claim it due to this being a bolt on.