This isn't a new concept, as it's used in gaming all the time.
The problem with this implementation is that it's not tied to the player's activity at all. Most all other unlock systems designed to ease you into increasingly more complex game design do so taking player activity into account. Some measure of skill level, collectibles, time devoted, or what have you is factored into how often to unlock this content.
Mario Maker doesn't give a shit how fast or slow people learn their tools. You're a fast learner and grasped everything within 6 hours? Fuck you, you don't get the rest of the content for another 210 IRL hours. Doesn't matter if you booted up the game for 5 minutes just to get credit for your log-in each day, thus learning nothing new about the editor each time consecutive day, and it doesn't matter if you're honing your skills for literally all of those 210 hours. It's a very unintelligent system and doesn't actually do anything to guarantee that you'll progressively learn more about the editor like they intended to. It's just a bad implementation of a common gaming concept.
In a typical Mario game the game got more complex/harder with each level, and each was unlocked when a previous one was cleared, thus ensuring to the game designer that the player has at least encountered the simpler game design. If one player spent 1 hour in one level because he/she found it very hard, the game will unlock itself slower than someone who blasted through that level in 3 minutes. Mario Maker's "system" forces the second player to wait a rigid amount of time (e.g., 1 hour) for the next level to unlock because Nintendo doesn't want to make a more dynamic unlock method, and they certainly don't want to unlock things "too fast" for new players who may find it overwhelming.
What would you suggest as a more dynamic method for this type of game? I am not thinking of a better metric.