Should there just be one sort of elf?

[Kae'Yoss]

there's no need for that kind of class-twinking.

You're wrong twice over. First, it's not necessarily twinking. If it was, using halfling instead of human when playing a rogue would be twinking, too.

And if it were twinking, it would be race-twinking Get your derogative straigt!

Let the traditional sub-race differences be cultural and cosmetic.

Have all the uber-powerups for the deep-versions (Duergar, Drow, Svirvneblin, etc.) due to the "inexplicable-magical-subterranean-supercharging-radiation." Make these powers transient upon leaving their realm unless they take a special feat.

 

[Remathilis]

I think WotC answered this question (in a round-about kinda way)...