I'm not so sure about the spaced repetition side of things. Out of curiosity I've just opened MathAcademy after not doing any lessons for a little over two weeks and all choices I have are for new lessons. I expected to see an ocean of reviews instead, since surely I'm on the verge of forgetting a lot of what I've learned.

Other than that, I have very high hopes for the future of MA. It's by far the best platform I've found for actually learning math.