I suspect it can't because the Wii Virtual Console is actually an emulator which naturally never had any Wii U functionality in mind when it was designed. It also seems that all Wii functions are sandboxed away from the higher Wii U level systems to prevent older Wii exploits. It's also probably a lot easier to enable Wii features in their own software environment rather than try to fully integrate it directly into the Wii U software environment.
They did it with GC mode on Wii, so this was expected. But porting Wii emulators to Wii U is not a big deal, I can imagine if exisitng Wii homebrew scene would have full access to Wii U OS they could do it in blink of an eye.
My Wii is practically a emu-machine right now, shared between legally obtained VC games and not so legal emualtion (I do play games I own though... mostly :D ). Damn Ninty, I takes ages before every next VC update and now it's practically dead.