Ugh, so some major hitches with writing up the bestiaries. Been swamped with work and it looks to be getting worse. I'll try and finish the Siguanaba as soon as tomorrow!
Personally, I don't want to see elves on Arcadia, if only because we have them in Tian Xia. I'd like to see either halflings or gnomes in Arcadia (I would would like to see Dwarves as the Avistan race in Casmaron)
I don't know how important that question of how humans got to Arcadia is really. IMHO it still not been adequately established why they exist in Golarion to begin with. I do get a sense that Syrinx might have been the dominant eastern Arcadian empire during age of the Azlanti. Now? who knows?
I also don't necessarily see an issue with stone age hunters in Arcadia. In Avistan, you have stone-age barbarians In the Realm of the Mammoth Lords, at the same time as steampunk elements in Alkenstar, and high magic in Nex, with a vast diversity of nations filling the spectrum in between. Arcadia (I think) is bigger than Avistan, so I don't see a problem with it being just as diverse.
I'm fine with running the gamut of genres personally, from stone age hunters to the Sky Captains of Machu Pichu from earlier :D