Right but the intent was to make a fresh 2D Mario because the existing line had grown stale. They gave them the time they needed, the game has been very successful, and you think they're going to move right on to the next thing? Maybe 3D Mario, but that's not 2D Mario's style.
Plus if they do something new with regular 2D Mario, with some separation between it and the Wonder sub-line, you could launch both on the same console without it seeming as saturated. But Wonder would presumably come first, while it's this lucrative and reusable.
And MM3 might show up at some point as well, but it's not as successful as the regular 2D line, so it probably won't be the priority. Plus Nintendo will embrace their internet infrastructure with Kart, Smash, AC, Splatoon, probably more 99 games, and the continued support of the NSO libraries. Online functionality isn't going to be a bigger deal to them than the sales difference between the 2D Mario lines.