You will not be able to get actual facts/details of unannounced phones until they have been announced.
All you can do is to assume that things will, indeed, improve.
If you want more than that, then talk to the analysts (IDC, Canalys, Ovum, Forrester, Gartner, Nomura, etc.) for their guesses as to device evolution. Their guesses can be quantified, but in general your own guesstimates are probably close enough, too.
In any case, you should probably attempt to write your software so that details like that doesn't matter (in order to be able to take advantage of the widest range of devices).