If it is $300 and has a mainline Pokemon game I see 30m-40m easily. If it gets third party support as good as the PS4 and Xbox One I believe it could sell 50m+. Right now Sony has such a strong foothold (and even Microsoft has turned things around) that I don't see it selling 100m+.
Worst case scenario I see is sales in the 10m-20m range. That is if the price is $400 or more with poor third party support past launch and no mainline Pokemon games.
I could be completely wrong though.