I plan to have the four elemental genasi as kind of aasimar races, but I think I'll keep them rare in numbers so they don't effectivly constitute a distinct culture in the world.
Other fey will be quite alien and supernatural and very inhuman. That's something where the blurring has to be kept very low to work. Nymphs may almost look like elves, but that's where the similarities end. Most other spirits will be closer to elementals and animal ghosts.

Beastmen have been quite high on my list for a long time.

One version, which I will almost certainly include, is based on a mix of Tauren/Cathar with the visual style of the Fearai from Primal. [1], [2], [3] Even though I want them to take the place of civilized orcs, I don't want them to be like either orcs or hobgoblins but something else. Something similar to a predatory version of the Warcraft Tauren perhaps. Earlier attempts didn't really result in anything but their general appearance, but this time I might try to come up with a unique culture and lifestyle for them very early on before thinking about where they are living and how they interact with their neighbors. That always just resulted in another type of civilized orcs.

Another thing would be something like Ratfolk/Shifters/Mithra. Shorter than humans, taller than gnomes, and also quick and clever, but not siginificantly advanced culturally. I think they could work similar to the non-cannibalistic halflings from Dark Sun.

I also want the primitive fish people that everyone has kept coppying for the last 100 years, be they Deep Ones, Kuo-toa, Murlocs, or whatever else you want. It's always the very same thing, and I like them. However, I think they would almost entirely monsters and pretty much never appear as one of the civilized races. Some remote coastal villages might trade with them, but that's it. They don't visit the markets or have any visitors to their settlements.

For the Underworld, I have planned goblins, grimlocks, and derro, but that's more like an alternative nightmare dimension inhabited by the descendants of mad cultists from the normal world, so I wouldn't count them among the civilized races either.

I think this might actually be more than enough races for a setting with a good variety of races and cultures, but they are all things I've been dragging along through my setting notes for years, and I still hope to come up with something fresh that could give the setting a unique character. Like planescape has the Gith and Dark Sun has the Thri-kreen.