Spaced repetition (workflow? plugin?)

Yes, you build app like that.

But I think Anki repetition algorithm is more complex than it seems. If you want something more complex you would have to come up with some internal systems that would do the math for you.

If you want some simple +1 week, +2 weeks + 3 weeks . That should be fairly easy.

Other spaced repetition topics on the forum:
http://forum.bubble.io/search?q=spaced%20repetition

There is even a fresh app