I think it would not be a good move, after PS3 has been in the market for a while, it is NOT so difficult to program for. Keeping the architecture similar allows faster game development (reduced cost) and gives automatic backward compatibility.
I for one would favor a multi-chip Cell based design even if it is a little bit slower than the rumored power7.
Cell has One normal CPU and 7 DSP chips, XBOX has 3 normal CPUs, IF Sony can have 3 CELL processors it will be 3 normal CPUs and 21 SPEs. It will leverage "both" investment in cell architecture from development point of view i.e. developer kit etc. and regular multi CPU architecture as well.
Increasing available memory per SPE and/or Per Processor would help as well.









