I believe part of the reason for the current limitation is that traditionally in D&D lore, certain types of creatures are immune or resistant to ceremorphosis, which would be hard to reconcile with the current plot. At least some changes to the dialogue/narrative would be necessary. We may get races such as Gnomes with time, but it's understandable that, given the extra work required, they weren't ready for early access.
That doesn't really seem to be the limitation here though, since dwarves are in the game but are considered "unacceptable" for ceremorphosis. It seems more likely that they just haven't finished working on the other races yet, so they weren't added. Got my fingers crossed that Dragonborn get added, would love to bring a Dragonborn Paladin character I've got to life in BG3