Nintendo didn't trail behind when it came to optical media, but made a conscious decision to stick with cartridges for the time being due to load times. Hell, the Playstation was basically the result of Nintendo looking to make a CD add-on for the SNES.
PPC vs. x86... well there's nothing special about x86. As a matter of fact, ever since I started learning about computer architecture, I've come to rather dislike the x86 (long before the Xbone and PS4 were even rumors). It's based on the antiquated CISC concept, but realizing that CISC is a bad idea, now have a RISC implementation of a CISC architecture. It makes sense to keep x86 in PCs because if you were to move away from it you suddenly lose all legacy support (hence why the Intel Itanium series failed when they tried to move past x86), but for game consoles that aren't already tied to it, I don't see the benefit. As for difficulty porting code because of different Instruction Set Architecture, I don't imagine it's a big deal these days as programming is done in APIs made by the console developers, not in assembly.
Also, saying that the Wii U is 3 Wiis or that the Wii is a Gamecube with a high clock frequency is like saying that a PC with a Core i7 is just 4 PCs with Pentium 4 processors, and that PCs with Pentium 4 processors are just PCs with fast 8086 processors.
And whoever said Nintendo should dump Miyamoto and those like him, that's the worst idea I've ever heard. Those people are the very core of Nintendo's identity. Jettisoning them to try to be more carbon-copies of the other companies in the market would just leave the market a more bland taste. If I didn't want Miyamotoesque things, I would have a PS4.