Since there will be a lot of Dark Elves roaming the streets, especially in the form of PCs, I expect DRIDERS! It would be amusing for a PC Dark Elf to get waylaid by a a Drow Underdark press gang, kidnapped back to the Underdark, accused for being a "race traitor", not worshiping Lolth or just not being plain EEEVIL…
Personally I think that specific and unique cross-class combos are unnecessary because it might become a scripting nightmare from a technical viewpoint and a simple gimmick at best. It will also present an opportunity to abuse the system. It is quite easy, especially if multi-classing is allowed, to make a single character…