The performance hit of tiling is small but once it goes past 16 or so tiles it can become problematic but no developers to my knowledge have ever attempted it and most of the time they opted out using 2 or 4 tiles. Why would a CPU be important for the purposes of rendering ? 

You don't know the definition of a "bottleneck" ... A bottleneck is something that limits potential on a system, not holds it back. 10mb of eDRAM is enough as it is for 720p resolutions using a tiling solution. A 720p framebuffer is around 7.3mb. The depth buffer is always of the same size as the framebuffer even when it's multisampled. 10mb of eDRAM is enough for a 720p 2x multisampled framebuffer with the depth buffer and can fit in 3 tiles.

So really when you think about it the xbox 360's solution is aguably better.

10MB does limit potential on the system; with 32MB it could do more.

On Wii U, a 1080p frame takes only half the eDRAM.

10MB of eDRAM is NOT a bottleneck once again. It doesn't limit potential, it adds more potential. More memory =/= Better memory

Despite the fact that the WII Us eDRAM has a higher bandwidth it's still not better by any means because the 8 ROPs on the xbox 360's eDRAM gives it the edge.

Yes, the WII U may be able to store a full 1080p frame but that's moot because most of the games on the WII U end up being 720p or lower therefore having 32mb of eDRAM was in vain.

32MB was not in vain; there are 1080p Wii U games, and with a 720p frame there is even more space left over for framebuffer operations or CPU/GPU tasks. 

I'd say that it was in vain ... The only 1080p games so far on the WII U is Wind Waker HD, Monster Hunter 3 Ultimate and Rayman legends. (Even though that one is 1080p on last gen platforms.) Most of the games ended up being 720p and lower.

Having to use an inefficient workaround just to render higher resolution frames (360) is a bottleneck. With more eDRAM, it could render the frames intact, and have the benefit of bonus space to use for other things.

How exactly is "tiling" an inefficient work around when it's very efficient ? There's not a whole lot of use than what you think ... Most of the graphical tasks are being done on shaders.

Actually, several eshop games are 1080p as well; Puddle, for instance is 1080p/60fps on Wii U.

And Shin'en have detailed many uses for the eDRAM, including CPU-intensive work and non-framebuffer GPU writes.

Those eshop games could likely pull it off without the eDRAM considering most of the games use low resolution textures ...

CPU intensive work means almost nothing for the most part when the GPU is the most important part to rendering. There are very few important workloads out today that would require fast access times. 

Even without high res textures, a 1080p frame, double buffered, is what? About 16MB?

And Shin'en certainly seemed to think the eDRAM was useful for more than just framebuffering, as they explained that they used the extra space for other GPU writes, and specifically pointed out that CPU and GPU both had access to it if they needed it.

They can still pull it off without the eDRAM ... These eshop titles are not texture or shading intensive ... In this sense they would mostly be bounded by the ROPs because the setup, shading, and texture mapping/filtering stages are mostly negligible and or insignificant.

And could you expand on their reasoning on why it would be useful for the CPU to have access to the eDRAM in a significant effect ?