So for the sake of argument let's say that Super Mario Maker sells quite well for Nintendo. It appears to be so far! That's rad.
If they were going to do DLC for the game, I sorta expect it would've been announced, since they were pretty up front about the DLC for Mario Kart 8 and Splatoon. So that leaves a sequel possibility. Which is tricky, because their options are weird.
If Nintendo carried on with this Super Mario Maker idea, where do they go?
Rerelease almost the same game but with... (Game Boy like) Mario Land and Wario Land levels? Include the ability to make levels based on the (not universally liked or remembered) Super Mario Bros. 2/Super Mario Bros. USA? Or craziest of all, 3D Mario Maker, allowing you to make levels based on the polygonal Mario games, which would be an absolute nightmare to make the user experience reasonable for? Alternately, will they move on to Zelda Maker, or Metroid Maker, game franchises that aren't universally beloved, where the game design needs to have a little more complexity and sequencing to it, instead of just being "platform around until you reach the end"?