I think that the 'sub-races' should be backgrounds, and could be wood-elf, deep delver, or nationality.
I also would like to see them avoid the 'half-' races and instead have a theme, limited to humans, that provides 'mixed' blood. That way you don't have racial bloat and can have half-elf, half-orc, half-dwarf...etc. Linked with the cultural backgrounds, this adds up to a wide range of racial options without adding too much to the ruleset.
The other cool thing that this does, and that I have recently been reminded is missing in so many RPG sessions, is a solid feel of nationality mattering. I would like to have something to base my descriptions of city streets that show the flavor of the folk... with cosmopolitan scenes with traders from Ragesia mixing with Dassen noblemen and Ostalin caravan merchants... but with description of characters instead of labels. For instance, Ragesia tends to wear black and red colors, furs, and have dark, swarthy complexions...
I just have a hard time coming up with a coherent feel for a world. If the culteral backgrounds included that fluff... then its a win for me!