Firstly, I wish you all the luck; this is a genuinely useful category of software and there simply aren't enough alternatives out there.

That being said, the big hurdle with SRS software is ... lack of content.

I wrote one too but gave up on it because creating the content takes too long.

What I'd like to see someone create is an open and free wikipedia-type-everyone-can-contribute-content project specifically for flashcards.

When I sign up to any SRS I want to be able to point the software to (for example) www.srs-commons.org/topics/programming/languages/kotlin, or maybe www.srs-commons.org/topics/history/south-africa/the-boer-war, or www.srs-commons.org/curriculums/us/grade-10/trigonometry.

Students seem particularly motivated to create a commons of cheating material, maybe they could be similarly motivated to add to a commons of study material.