What people are forgetting is the major advancements in technology we have had. Let's use Moore's Law that states and I quote from wikipedia " is the observation that, over the history of computing hardware, the number of transistors in a dense integrated circuit doubles approximately every two years."
Using this: http://en.wikipedia.org/wiki/Power_Architecture
Look at the history, there is a constant line of upgrades with PowerPC and the last major one for x86 is x86-64 (I wouldn't call multi-core processing an upgrade, multi-CPU ability has been around for ages, i've seen boards with 2 P4s in them.
So yes, I see Nintendo absorbing the Wii U in it's new console in 4 or 5 years with the next portable running on the same architecture for easy porting. Power PC is here to stay and chances are it will be running on a higher clocked hex core or something for their next console