Just like that it's plausible that IBM is making a custom PowerPC core for the next generation of consoles, I think it's also quite likely AMD is cooking some customized shader architecture for next gen as well. Perhaps similar to GCN but with some of the bulk removed.I read awhile back that Xenos is supposedly not VLIW-based. Considering the supposed inefficiency of VLIW5 once DX10 came out, I think it's plausible Nintendo came up with something of their own. Not guaranteed, just plausible.
Even if they're not, I don't expect the Wii U to have schoolbook VLIW4 or GCN implementation.