It's definitely strange. From what I have seen, hackers have been able to run GC games near-flawlessly on Wii U via Wii mode, so "emulation" wouldn't be an issue, I would think? They could have run them like the Wii game downloads you can buy on the eShop. Maybe it's something different, like the triggers, as stated above, I dunno.
I imagine it could come to NX, but I really don't know. If Nintendo was smart, they would launch NX with a whole mess of VC games; some Gamecube and Wii Games the entire Wii/Wii U/3DS library of VC titles and then some. Heck, throw in Dreamcast even! But, Nintendo doesn't always do what seems logical. They do things their own way, regardless of the reception. Yet, I hope they realize that if they want to make money on the NX, then they'll really have to offer up what their fans want, bringing out the big guns. We'll see in due time. No later than E3, hopefully.