I've thought about doing this too - and there are certainly things that are worth rote memorization on guitar. But my experience has been that things stick a million times better when I learn them in context and really focus on using them, so I'm unsure how useful implementing spaced repetition would be vs "just play yer guitar".
That said, the notes on the fretboard is well worth the effort of rote memorization. I found the technique in this video[1] worked absurdly well for me. Years and years of only knowing the notes half-assed and not very well on the middle three strings got absolutely busted after doing this for a few minutes every time I was waiting on a build or something. I can nearly always find a note now, I'm not quite to instant recall but have substantially more ability in this regard now.
A place where spaced repetition might be worth it is in memorizing all the triads or keys, which is good to have instant recall on. I have these decently in my head but usually have to "convert" from a nearby chord in C major for oddball ones, which is fine while practicing but not what you'd want for performance.
> I'm unsure how useful implementing spaced repetition would be vs "just play yer guitar"
There's no reason you can't do both: Make flashcards that have a few bars of music on the front (tab or notation, whichever you use), and then actually play the music when the card comes up to figure out how the review should be rated.
Absolutely - that sounds like it would be a good approach. The main point I'm trying to make is that (at least, in my experience) there at least two classes of "guitar-related information," one that's amenable to rote memorization - like the notes on the fretboard, music theory "facts", etc - and another category where the information sticks better and in a much more usable way if it's learned in context. I would think that "ear training" (specifically interval identification) would probably be somewhere in the middle - you could benefit simultaneously from the "rote" memorization and also apply it on the fretboard).
I spent a long time just playing the different 3nps shapes and never had them really soak in until I started picking small chunks of them out as useful during improvisation and really focusing on them while playing over loops or just noodling.
What would be really awesome, especially if you're improvisation focused, would be some cards that have a short backing section attached to them - so that you can hear some musical context and then work on some small chunk of information (like 2 or 3 strings of a scale). Something like that would probably the best of both worlds and I bet you could learn a lot of material really quickly that way.
That said, the notes on the fretboard is well worth the effort of rote memorization. I found the technique in this video[1] worked absurdly well for me. Years and years of only knowing the notes half-assed and not very well on the middle three strings got absolutely busted after doing this for a few minutes every time I was waiting on a build or something. I can nearly always find a note now, I'm not quite to instant recall but have substantially more ability in this regard now.
A place where spaced repetition might be worth it is in memorizing all the triads or keys, which is good to have instant recall on. I have these decently in my head but usually have to "convert" from a nearby chord in C major for oddball ones, which is fine while practicing but not what you'd want for performance.
[1]: https://youtu.be/PJddQ6Q0UDo?si=4dmR7_tlsWIhgvYg