The Warlock of the Stonecrowns adventure mentions an underground city which
MAY be inhabited by elven followers of Azrai (or may be actually a goblin
city - no one knows for sure), and there have been several letters on this
list discussing a "darker" version of elf for Birthright. I've got the
letters saved to disk somewhere, and if I can't find them, I'm sure somebody
else has them.

IMHO, I think darker elves would be ok, but I would avoid getting too
"drowish". I really like the unique flavor of the BR setting. I think that's
what makes it stand out from other TSR products.