Super Mario Maker will have an artificial cap on how many levels you are able to upload — the move is most likely to ensure that people are only uploading quality levels, compared to endless iterations of World 1-1.
While it had been briefly murmured about, a screenshot surfacing today (above) indicates that for each medal you receive you will be able to upload 10 more levels. Medals are earned by receiving high ranked reviews from the community after they complete it. The image shows 40 available slots with the player having four medals — the deduction is possibly 10 per medal, but the base amount would alter that equation. Super Mario Maker will be released exclusively on Wii U this September.