the gamepad input doesn't work because of technical limitations, vWii mode communicates via bluetooth, that's around 2,4Ghz wifi, the WiiU Gamepad communicates via around 5Ghz wifi, so in order for the vWii to understand the Gamepad input, they would have to rewrite some IOSes
I'm not saying, it would be impossible, Ninty could certainly do it, but they may be focusing on other things first and don't want to work on old software
and what is up with the GBA VC? where did you get this info? this is a list of GBA VC titles on the WiiU:
http://en.wikipedia.org/wiki/List_o...i_U_(North_America)#Nintendo_Game_Boy_Advance