Henadic Theologian
Legend
Aasimar seem like the most obvious to add, as they're the counterpart to tieflings. Selfishly I'd love to see genasi there though, as they're my favourite player species.
(though I don't really view planetouched as their own species, more members of other species who have been touched by either planar or elemental magic)
There is a major pattern to the choices of race.
The first kind is classic Tolkien/early D&D inspired, Elf, Human, Dwarf, Gnome, Halfling, and Orc.
The second are hybrid "monster" races, Goliaths (Giants), Dragonborn (Dragons), Tieflings (Fiends), Aasimar (Celestials), Genasi (Elementals), Changelings (depending on version Doppelganger/monsterous or Fey). Now that I think of it, the weird lore shift in MotM from Doppelgangers to Fey could have been to bring it more inline with folklore so they could use it a the Fey hybrid race in a One D&D PHB later. Maybe in One D&D MM Doppelgangers will be fey now too, a change I actually really like.