How many available races is too many, Veeky Forums?
In my setting, a major theme is supposed to be that things are changing - technology, magic, society; the overall feel is going to be more Age of Exploration/Reformation/early Enlightenment than Medieval/Renaissance as most D&D settings are. One of the ways I want to reflect this is the decline of some of the common races (elves, dwarves) due to rejection of change and traditionalist natures, while some of the uncommon (gnome, triton) and monstrous (goblinoid, kobold) races are on the rise, founding their own nations and interacting with others around them in a somewhat more amicable way. At the same time, I don't want to eliminate the classic choices entirely, since the theme is the transition itself, not starting on the other side of one.
Problematically, though, that's left me with sixteen races:
Dragonborn (here, descendants of half-dragons), dwarves, elves, gnomes, goblins, goliaths (here, half-giants), half-elves, half-orcs, halflings, hobgoblins, humans, kobolds, orcs, tieflings, and tritons (descendants of human/merfolk couplings).
Tieflings could be eliminated as a noteworthy race since in my setting details they'd really only be common in one nation, but that still leaves me with fifteen races, not including subraces.