Assuming the hardware sees the light of day about six years after the PS3 launch, or November 2012, it should be entirely possible to produce a $399 console that runs 1920x1080 native render resolution at 60fps. Anything beyond that would probably be overspecced assuming HD broadcast standards don't change in the next three years (unlikely considering how long it took for the transition to 720p/1080i) and the typical TV in the average household is a 1080p HDTV.
Shouldn't take more than 512-1024MB of VRAM and 1-2GB of system RAM, assuming hardware designs stay with the standard CPU/GPU architecture.
The only thing I can think of offhand that would require higher specs would be if SCE plans on making a stereo 3D video output system meant to be played on 120hz displays which could significantly increase the video processing overhead assuming a smooth 60fps (x2 progressive fields) remained the target.
Beyond the video specs, it's all speculation as to what else the next generation will bring to the PS line of consoles.
If SCE tries to sell Joe Public another $600 console (or more) on debut, they haven't learned anything from this generation and I expect it to be met with the same reception as the PS3 on release.







