While I don't see Nintendo doing this (with the fully justified fear of hurting console sales), I could see a full-out Animal Crossing game be immensly succesfull. Mobile games profit from attention rates, and Animal Crossing is ideally constructed for such, essentially a (much) higher quality Zenga game.

I could see people checking by for years, with well-timed purchasable items (chrsitmas decoration, etc...), close to 1 million $ per day, for 2 years or more, does not seem impossible.

Fire Emblem, on the other hand, would need to be heavily restructured. The safest option would probably be to give it a structure similar online structure to Clash of Clans/etc... , and go whaling, making sure that paying can somehow distinguish the person from other players..

freemium Mario with a Candy crush system.

5 lives, 1 recovers every 15-30 minutes. Bunch of levels, etc etc. Add Micro transactions, advertisements for NX and other games, and get easy money.

Would make sense, economically. I don't think Nintendo has a mario game planned, though.