Nobody has said anything about the TEV Unit from Flipper being the 'secret sauce'. If Latte is using fixed functions (and I believe it is) then the TEV Unit will have to have evolved considerably to prevent the Wii U from having the same problem that the Wii had with ports. Hollywood gave the Wii a nonstandard rendering pipeline making ports impossible. We know this isn't the case with the Wii U because developers have found it easy to port PS3 and 360 games to the console.
And if it isn't using fixed functions and Latte is indeed a 160 ALU GPU then I'd love someone to explain how Bayonetta 2 is possible when the power draw is so low and why the ALUs are also twice the size they should be. Fixed functions of some description explain the size of the ALUs and the low power draw.
It doesn't matter how efficient the shaders are, what we've seen of Super Mario 3D World, Bayonetta 2, Mario Kart 8, X and SSBU shouldn't be possible on a bog standard 160 ALU GPU.
You can call it secret sauce, Nintendo magic, Navi fairy dust, Pikmin hard at work or whatever you want but there's plenty going on under the hood that we're completely unaware of. Again, if you have an alternate theory to fixed functions making all this possible that also explains the huge ALUs and low power draw then we're all ears.
Just my opinion, but you won't like it. There's nothing there in any of those games that makes me think "wow how did they do that on Wii U?" As a result I don't think there is any special sauce involved at all.