With the DSi, there is no gifting feature, but you can always download DSiWare and transfer individual titles to the 3DS. But, A) It's a pain in the neck and B) 3DS has that whole "cleaning the fridge" mindset when it comes to DSiWare. Also, I have virtually everything good on DSiWare.
With the Wii U, the Wii U version of the Wii Shop does not support gifting (Yeah, I know), so, once you've transferred everything, you're boned.