Legacy: Just add some more stuff from the past games and one or two more old friends return. Aerie is most obvious. Minsc should be with his witch, she's not very old, and very easy to justify showing up anywhere; just generally wanting to help and protect people from abuse like she suffered, stand by who she's realized are her real family (Jaheira & Minsc), or just having a bit of an explore and wander as her religion pretty much commands her to. And if you need to make her cooler - even though Minsc and I think she's pretty cool already - then sure - give her back her freaking wings (I would make them magic wings that can appear and disappear since she doesn't consider herself truly Avariel by this point), or the ability to summon Rocket Raccoon - sorry; Chiktikka Fastpaws. That would tie the whole trilogy together, but then possibly you could also have a descendant of another character, or another elf from BG1.
If it’s too much to add them to the main game at this point, maybe have a separate little campaign where Jaheira sends a bunch of oldies on another mission, with Aerie going along as their carer.
