Pretty sure there has been multiple posts on this, but ya, changeling (don't think they made it to forgotten realms lore if not Gensai & Eladrin).
Genasi are a big part Mulhurond lore. I believe, since the djinn ruled the place for a long while. Changelings and Eladrin can reasonably show up anywhere, really.
No clue, just remember Gensai being in 3.0 forgotten realms campaign guide.
I actually own the forgotten realms campaign guide and players guide for 4e, list of races that made it.
Drow was introduced for 4e
Gensai was introduced for 4e
following were marked as common races, being a major forces for FR:
Dragonborn
Dwarves
Eladrin
Elves
Half-Elves
Halflings
Humans
Tieflings
Then supporting races, which was just claimed as the other races
Gnomes
Goblins
Lycanthropes and Shifters
Half-Orcs and
OrcsDevas (Which if I remember correctly are just aasimar)
Goliths
Shades
This is where I'm getting Eladrin for FR, I know they got a make over in 5e but since they were introduced in 4e I'm presuming they are still their. Now, warforged and changelings as far as I know didn't make it over, but I don't have 5e stuff or read any books.
Seeing a changeling race though, that would be pretty epic, probably more than seeing a donkey.