Is there any reason to not go for the term "ancestry"?
I see nothing good coming out of splitting the terminology, and like it or not, Pathfinder 2 was first to coin a term here.
Because naming things is a hard problem, and we're not nearly at a point yet where the mechanics have been defined enough that the right name is a concern.
'Race' is simple and clear, and implies a direct mapping which can include things like half-elves and half-orcs. It does, however, have a lot of people try to find ways to make it equivalent to race relations in the real world, despite it not being the same thing.
'Ancestry' implies a 'pure' mapping because it stretches into the past (see: Draconic Ancestry for Dragonborn). Thus there would be no half-elf or half-orc ancestries, but only human or elf or orc. That in turn means you would need to be able to define multiple ancestral types for a given character, which means you need mechanics for combining human and elf ancestries to get the equivalent of the half-elf. Pathfinder uses a human base and then adds a racial feat to get there, which means it's not mechanically compatible with the 5E approach. That may not be what the game designers want to allow for.
'Species' sounds like you have a bunch of bodies pinned up to a board in a scientist's lab somewhere. Frankly, it doesn't fit the aesthetic of pseudo-medieval D&D settings.
'Breed' sounds like you're talking about your pet dog.
Lineage might work, though it's somewhat close to Ancestry in implications.
Kindred is maybe. Folk is probably too 'casual' a term. Descent, Origin, Forebears, Heredity, and so forth. Each suggests things slightly different about what the mechanic is intended to convey, and how it's intended to work.
Basically, while I like Ancestry as a term, using it just because Pathfinder adopted it seems liable to introduce confusion for those who would use the term in both systems, since they would not work the same way, mechanically. Any other choice at the moment is putting the cart before the horse, because, as I said, naming things is a hard problem, and is not an urgent issue for the board that's just brainstorming for mechanics changes.