I've already poked at Kulyok a bit about this idea, but I found this forum and thought I'd give the idea some fresh air.
Well, it starts about.. eight long years ago(?) when Icewind Dale was first released. I was still a naive but enthusiastic youngling in the Realms. However, I knew the longevity of elves, and as a sort of vague attempt at tying the two games together a little, in my first group I created everyone's favorite elven enchanter, Xan.
Much to my surprise, partway through the game, I found and read the journel of Erevain, and was very much surprised to find reference to his cousin, Xan. I firmly believe we should take this as a divine sign that expansion is called for.
I admit I haven't gotten around to playing the Icewind Dale NPCs yet, but I seem to recall Kulyok mentioning some ties to Erevain in it, so someone will have to enlighten me. But at this point, I would be very interested in seeing Xan, and possibly Erevain as playable characters, maybe among others.
I'm aware that there would be a level gap for Xan between the two games, and that Icewind Dale mods are not as popular as Shadows of Amn, but I bet we could figure some things out. And hey, you asked for ideas.. let's see if anyone here shares my passion for this at this time.