Take a look at this interview snippet with Miyamoto, pertaining to an eShop release for Mario's next big adventure.

"I think we will only put 'bigger' games on the eShop if there is a real meaning for 3DS or the idea. The main Mario titles will always be created for packaging, but if it was meaningful and always there, then maybe we would put one on eShop."

Now, Super Mario 3D Land didn't hit the eShop, and that was the next big Mario game on 3DS. With that said, it sure seems like Miyamoto knew that the idea was being toyed with for a future Mario outing!