Yes and no. A Mario title like Smash Bros is supposed to be would not be good at all. Two Mario games that can be linked and content unlocked. Yah great idea but two Mario games nearly identical would not be a good idea. Nintendo doesn't often release console ports simultaneously. Sony has tried with little success.
Also again I don't think Mario has ever been necessary for WiiU's launch. But GTA5 would not be sufficient to push WiiU without some strong exclusive software. I can tell you right now a port would not drive new hardware consumers want new software and unique experiences. Unless Nintendo secured some exclusive content for GTA5.
And shows a tangible improvement in graphics, otherwise people will mostly buy it for their PS360 and wait for the DLCs with that content.
Otherwise I agree that GTA is not enough for Nintendo to have the succesful launch they want. It could convince some non-Nintendo gamers to purchase the console given the above conditions, but they also need a game that caters their actual customers, and for that, a 2D Mario could do wonders.
I see know reason why it would not have much better graphics that the current HD twins. Extra content? I have no idea. I doubt it though. It will probably be like buying it and playing it on a suped up PC. Other than that I doubt anything will be different. It would be cool to have some Nintendo characters here and their randomly. Like My little pony in Skyrim!
If Rockstar/Take2 bring it to WiiU it's obvious that the graphics will be better, if only because being it more powerful and having more RAM could mean better framerates. But I said a tangible improvement, and people can't notice the framerates in pics or press videos (at least most of them). But they can see better lightning/shadows, a more distant horizon or even the game running natively at 1080p against being 720p or lower.
And regarding the Nintendo characters being in a Mature game... well, you could go through a street and see a Marco&Gigio Plumber's shop or something like that given how Rockstar works, but not actual characters.
Please excuse my bad English.
Currently gaming on a PC with an i5-4670k@stock (for now), 16Gb RAM 1600 MHz and a GTX 1070
Steam / Live / NNID : jonxiquet Add me if you want, but I'm a single player gamer.