Hmm, that could be interesting. I'd go with the Denisovans, who were already living in close vicinity to Beringia in 41,000 BC IOTL, writing such an ATL in a similar manner to Stephen Baxter's Northland Trilogy. Of course TTL's 'Columbian Exchange' (although I very much doubt that Christopher Columbus will be around ITTL to play a role) will be far more severe than OTL's, with the very real possibility of wiping out all of the native American Denisovans, but hey, it'll be interesting while it lasts...