While I'm not saying the second CPU rumor is true, that diagram doesn't show the DSP or I/O processors and those are confirmed to exist.

He says the diagram just englobe CPU/GPU, substrate/interposer and memory... nothing else.

His supositions...

CPU: 5x6mm^2, PowerPC 47x, 3MB eDRAM L2.
GPU: 14x12mm^2, 40nm, 32MB eDRAM, RV740.
RAM: 4x512MB DDR3.

The Wii had an ARM9 CPU (which handled I/O, security systems and low level firmware) and a DSP intergrated into the GPU package. the ARM CPU was embedded in the GPU and the DSP was embedded into the 1T-SRAM that they used for VRAM.

I would say it's likely that they did the same with the Wii U so that GPU package likely not only includes the GPU and a large chunck of eDRAM, but also an ARM bassed I/O controler and a DSP.

What does this mean if true? I'm no tech-head, so I have no clue :P I'm guessing it'll leave more memory for the WiiU to use?

It think it means that the PowerPC-CPU can be fully used for games, because the OS runs on its own CPU in background and don't "steal" any processor power.

Because it is mentioned as IO-Chip I am curios if that means that even the Datastream between Wii U & Gamepad runs on the second CPU, so the PowerPC is really only for the games. Would be great.

Does that mean it'll be able to "add more things" in the game? More enemies on screen and stuff like that?

A 2nd CPU, with different architecture too, what's worse, for the OS just doesn't make sense: POWER is a very scalable architecture and simply adding another core to the CPU, if necessary, would cost a little less for the total cost of the components and a lot less for the overall cost of SW and HW architecture design, while delivering far better performances, as the OS reserved core would communicate far faster with the other cores, and without the need of a translation layer.
Different architecture for the OS CPUs are used, afaik, in some massively parallel supercomputers, but they are designed to work at their best on applications quite different from videogames, and they require to write programs specifically for them, this would make ports to and from them more difficult and expensive. An example: http://en.wikipedia.org/wiki/IBM_Roadrunner

Edit: PS I just read what some of you wrote about the ARM CPU used in the Wii, that's quite a different thing, it's used as a coprocessor or a HW accelerator, programs running in the CPU just feed to it some calculations it's best at, just like they do the same thing with the GPU. So a ARM CPU can be used in Wii U not to run the OS, but simply for the same purposes it was used for in the Wii.

Hm, isn't that 4750/4770 equivalent? Doesn't seem to fit in power envelope (though, performance is in line with e6760 rumour).

The performance showed for now is not E6760 equivalent... it's more RV730/RV740 with low clock.

The RV740 fits in the power envelop... more like a Mobility Radeon HD 4860 (RV740).

But can be a E6770 with really low clock (400Mhz).

30mm'2 for a three core 45nm PowerPC with all the cash ram etc.. that is VERY optimistic