Well, a lot (not all) of the things a Wii U can do, a modded Wii can also do (in a lower level, of course)
I'll make a list:
Wii U Hacked Wii
New Super Mario Bros. U | Newer Super Mario Bros. Wii + many more NSMBW Hacks
vWii Mode | The Wii Itself
Mario Kart 8 | Mario Kart Wii Hacks
99c 3rd Party eShop Games | Homebrew Games Chatting with friends on Miiverse | WiiChat Homebrew
Miiverse | uhh.. I dunno. comment what you think
The list goes on! Comment more to add to the list!
I'll make a list:
Wii U Hacked Wii
New Super Mario Bros. U | Newer Super Mario Bros. Wii + many more NSMBW Hacks
vWii Mode | The Wii Itself
Mario Kart 8 | Mario Kart Wii Hacks
99c 3rd Party eShop Games | Homebrew Games Chatting with friends on Miiverse | WiiChat Homebrew
Miiverse | uhh.. I dunno. comment what you think
The list goes on! Comment more to add to the list!