I'm currently learning ASL, which along with other sign languages would greatly benefit from a spaced repetition platform like this. Maybe an expert signer can weigh in here.

The interesting differences between, say duolingo and what a sign student would want to see:

* Flashcards are okay for some signs but plenty of signs are much better seen animated

* some signs are complicated and you need to see the whole signer from waist up; others are simple enough a simple image would do

* Short youtube embedded clips are okay except loading times are aggravating

* clips should be high res; some finger actions are small and detail can be hard to see

* there are variations between different sign languages, eg BSL and ASL

* source material is hard to get but there are a few sign teachers working on their own, one video at a time. They might be interested in partnering.