It's not the type of CPU which is the problem... IBM PCs (x86) emulate heaps of different other CPUs, such as PowerPC, 6502, Motorola 68000 etc etc.
The PS3 is not that much more powerful than the 360. In order to emulate a system, the processor, gfx, sound and all the interconnecting systems have to be emulated. This is generally done by one CPU on the emulating system. Therefore I highly doubt that it is possible.