From Scott's other posts around the forum, their design emphasis is to be as approachable as Mario Maker, but able to make more stuff. Not so much to be a simple Unity/GameMaker Studio.
There's been a mention that the idea is specifically to not have any programming needed, and I think while they'll probably have a lot of editors and "remixing" capability within the system, they're not likely going to have any accessible programming languages.
Maybe a light event-style system at most, but that's just me guessing.
ScottTykoski (one of the people on the Game's team) is very active on here, and while I know he's super busy getting stuff ready, he might chime in to correct or add anything I missed above.