As others have already said, you're not required to allow any race in your homebrew setting. Heck, half my settings only allow humans and that's it (not DnD though).
That being said, if you go for high fantasy, I think elementals (aka genasi) always add quite a bit to the lore and I would add at least one scaly race. Be it Dragonborn, Lizardmen or Naga and maybe a beast race if it fits your world.
But it really depends on the kind of world you want.