I just wanted to mention that when I did a search in the Wii U eshop for "demo" 9 3DS titles appeared. There were screen shots but no video.
I'm sure this is only the start of how the eshop will work together on both systems.
Steam/Origin ID: salorider
Nintendo Network ID: salorider
PSN: salorider
3DS Friend Code: 4983-4984-4179