I've been reading this thread and the NeoGAFs one for a while, and I believe that some points might be missing on some of the GPU die shot analysis. While I'm no expert on determining GPU logics only by looking at die shots, there are some rumors and facts that do not fit on those analysis.
First, there were several rumors and leaks last year, before Wii U launch saying that it was R700 based. Then, there was an AMD representative interview saying that Nintendo did not customize their design, and just licensed it. Latest, there was an developer who said that it had tesselation capabilities. Well, if you look at R700 and R800 options, there is no 160SP part available. It is 80 or 320SP. And in my point of view, changin SPU count is a customization, and this was ruled off by the AMD rep. The only customization that I believe Nintendo did was adding the Renesas eDram to the GPU logic. For me, its either a vanila HD4650 or HD5550, with no Nintendo secret sauce at all. And the tesselation abilities points more to the later option.