Obligatory Mario Paint suggestion.
In all seriousness though, I'd guess Art Academy has a lot more cache as a brand at this point than Mario paint, so I'd wager a game from this series makes sense, at least for tablets. Have some basic colors/paintbrush types, a few introductory pictures, and then a free paint mode. Offer extra paint tools & new paintings for extra.
Those Mario Vs. Donkey Kong games are perfect for mobile, although i'd guess they'd do that as a "free" app with a few starter levels, and then offer "level packs".
Brain Age also seems like an obvious choice for mobile, and I don't recall seeing anything from that series for a long time.
I'm waiting now for them to produce a game similar to Simpsons: Tapped-out. They could just have you create your own Mii character, and have you build your own city with themed buildings/characters from the various Nintendo properties. I'm sure a bunch of people grimace at the thought if you played these games, as they're filled with gated items that you can only feasibly get by paying money to get the premium currency, but they gotta reel in the whales somehow.
What i'm really curious about is if there's opportunity for there to be cross-over, cross-play, or cross-buy potential for some of these, because I'd be surprised if some of these games didn't also end up with a 3DS version at some point. I'm guessing not though, I'm fairly pessimistic about Nintendo's current ability, much less interest in doing so.