Three assumptions:
1. That we're talking about PC-playable species here, rather than whether a species should exist in the setting at all.
2. That we're talking about just the core game here and ignoring setting-specific considerations.
3. That the core game isn't tied to a default setting.
Given that, for the core I'd go with the original seven minus Gnome, leaving Human, Dwarf, Elf, Hobbit, Part-Elf and Part-Orc. All the other options plus more could be tied to specific settings and used as differentiators between them. For example:
FR - add Dragonborn, Tieflings, and other high-magic species
Eberron - add Gnomes, Warforged, and other species that deal with tinkering with stuff
Planescape - add Genasi, Aasimar, and other extra-planar species
New Setting X - add Orc, Kobold, Goblin, and other very low magic species
And so on. That way, each setting has a feature to truly call its own while those who want to can still port species from one setting to another if desired, or if building a homebrew setting. And non-playable species on a given setting's list could revert to being monsters, opponents, or just wierd stuff met during one's travels; or maybe not exist in that setting at all.