TwoSix
Dirty, realism-hating munchkin powergamer
That's doable, especially since ad-hoc creation or modification a feat is easy.In each species description, organize the traits into feat-size thematic clusters. Every playtest species has three feats worth of design space (not including the intro of Creature Type, Size, Speed, Lifespan, and one prominent Language).
So if a player wants a multispecies, pick three species feats from any of the species already described. There is no need for extra page count except for a brief section that allows a player to do this for a multispecies character.
Multispecies rules are easy and brief.
I suppose other people might have problems with it since it means most PCs will end up as a multispecies, but that doesn't bother me any.