Just came to my mind that how about qwerty but with added functionality combined with auto-completion and prediction. With this I mean that keyboard would adjust slightly it size on letters by what it predicts to come (of course by analyzing all your writings on device and calculating occurance index and giving weighted index for words to come). Or has it already been done? It would bold and made couple of pixels wider and higher those letters that it predicts for. Not too much butt settle amount.

I mean that it doesn´t make any sense to have letters equal size (on touch screen) if hard fact is that every language has it´s only certain letters that are mostly used. You can´t start changing letters place even-thought it might mean that user could learn to type faster but it´s pretty obvious that end user would get frustrated quite soon if you throw something too new and weird on this subject.