I'm hoping that a Cell-type CPU isn't in the works for the PSP2... Since the thing wasn't designed to run at low clock speeds, nor at low power consumption.
Even assuming we cut the SPEs to 4, and migrate to a 32nm fabrication process, we're still looking at probably 20+ watts. Reducing the clock speed would obviously cut it further, but there's only so much you can cut it by before it becomes pointless. Contrast this to the sub-5 watt range ARM or mobile MIPS CPUs run at, and perhaps you can see the problem.
Personally, I'm hoping it uses a more conventional CPU, and then includes some GPGPU functionality on the GPU; that way it can use the GPU for handling HD video, so you won't have silicon going to waste (and still wasting even just a little battery power) while playing games; it's a broadly-known fact that most of the Cell sits idle on the PS3 while gaming. So having the same power draw that isn't being used on a mobile device makes no sense.