I got the new OneNote both when upgrading from 8.1 and on a clean installAha, that's probably it: you have to upgrade a previous Win10 build to get the new version. Makes some sense, finally, thanks.
And I hear you re: the new version. Good thing is, I've been using OneNote 2013 anyways so it doesn't really matter to me. Incidentally, is it weird that the best touch-based OneNote is the iOS version? Yes, I think it is...