T2 didnt release gta on the wii or any other nintendo systems simply because they dont think sales would be good enough. Do you seriously think gta would sell tens of millions on the nx?
Wii mote would have been difficult to program an open world game that does so many things, so I think it was the controller that was the reason they did not do it. If NX has buttons GTA V would work well with it and with enough power like having a Tegra X1 it would be able to handle GTA V very easily.
Controller mapping even for a wii mote would be painfully easy relative to actually trying to get a game like gtaV to run on the wii, and I'm more inclined to believe that would be a bigger barrier than something trivial like an input device. Take Two didn't release it on the Wii probably because it wasn't technically feasible without massive downgrades across the open world. Which is where quality control comes in.
Whether or not that's true, I still can't imagine a handheld gta being a big deal for Nintendo unless there was something incredibly novel or unique about it.