The following musings are about sub-races in general, not just elf sub-races:
There should still be "sub-races". Shield Dwarves should not be the same as Gold Dwarves.
But I guess it's alright if they all share the same basic ability tree. After that, there should be sub-racial/cultural differences, especially for the Forgotten Realms (and, frankly, for every campaign that could use them, including homebrew campaigns).
I like how subrace and "culture" (= home region) interact in the Player's Guide to Faerûn:
For every race (not subrace), there's a number of home regions. Every home region has a list of sub-races that are common/possible there. Depending on your home region, you get access to regional feats, get extra starting languages (the regional languages), and some bonus equipment.
I could see something like that in FR 4e (and maybe 4e in general):
Races have sub-races, but the abilities are the same (or maybe the initial abilities you get at level 1 vary slightly, like sun elves getting +2 Int instead of +2 Dex). Then there's different cultures (usually a regional/racial combination, like "humans from the Moonshaes" or "elf from the Moonshaes") that sometimes require specific subraces (maybe there's "moon elf from Evermeet" and "sun elf from Evermeet").
This culture will have some impact on your abilities (like extra class skills, skill bonuses, weapon proficiencies, extra languages, and so on) and grant you access to cultural feats you can use to adapt the character to his culture.