Even if the ability to edit the game binaries doesn't exist, this could be resource replacement, right? ROM hacks without new features, basically. Can edit levels for games, do texture replacements, and so on.
And of course I have to tentatively mention that while most game-based exploits rely on changing external data to be loaded (malformed save usually), if the resources for the game itself could be swapped there'd be a hell of a lot more things you could feed a game. Of course if the Wii U has crap like NX/ASLR and junk it's not going to be as easy to get code running as on the Wii, and if the stuff is sandboxed that's another hurdle for actually modding the OS, and people would need one of these chips to get started... but still. It's a thing?
I would be well up for a bit of resource ripping but given the wii used full disc encryption and others are getting into the file signatures (the 360 did a bit of this in XGD3 titles hence overburning/cut off not being an option any more) I would not hold out much hope. Also given games are fans of high level scripting languages (we even saw lua used in commercial games on the DS) I imagine the security people would have not allowed arbitrary code to come from the assets side of things (though such a thing would be my first port of call on the DSi and 3ds if they finally close the overlay option). That said even the non obviously turing complete scripting options of games allow for some serious changes, sometimes on a par with things that would previously have required ASM hacks, so it would be really nice.
As for the "we all hope Nintendo bounce back thing".... I dare say if Nintendo do experience a failure this time around it would not be an unjustified one.