You know what, unless handheld screens explode in size, it won't take too long to achieve HD quality, because the screen is small.
I mean, if you look at 1440P quality movie on 50" monitor at 10cm distance, the visual is crap. Handheld screens are really small and yet they are viewed from like 30cm away, so 640x360 would be HD enough for handhelds IMO.