All PHB races are confirmed for the final installment of the game. I hope for some more.
And yeah, usually ceremorphosis could be used in gnomes(and other creatures that usually are not suitable, like dragons, lizardfolk, etc), with a high mortality rate. When it succeeded you create a gnome half-ilithid called Gnome Ceremorph
sc:
https://forgottenrealms.fandom.com/wiki/Gnome_ceremorphOthers like duergar, centaurs, dwarves,halflings could be hosts for a tadpole, but they invariably died, if you follow the usual lore of D&D5e. I do not know how´s going to be with dwarves and halflings in the game.