Combination of SRS and memory castles.
For the thought experiment, instead of flashcards, suppose you have a stack of cheatsheets. You wanna memorize them. You go and put the cheatsheets in a memory castle.
In mindspace, you can alter the cheatsheets – the words are no longer confined to A4 sheets, and art can be three-dimensional and include the sense of touch.
Obama's insight about blue suits can be represented by Obama wearing a blue suit, e.g. Though the presence of a person would be overpowering, so persons should only be used for important insights. A framed Obama?
For advanced potential, perhaps add smell to different rooms – if you focus inwardly on really feeling that smell, you kind of will smell it, regardless of what your flesh nose is sensing. And then, turn your attention to the room, and it should come back more easily. To mint new memory objects, it may help to go in meatspace to smell the appropriate thing for that room.
For example… a Chinese-styled room, smelling of chai tea. Go smell some meatspace chai before even trying to envision it (because memory retcons itself, you may cause details to disappear forever).
Instead of words, you can have objects. Suppose you've read a book and written notes from it. Eventually these notes become a box of objects in your memory castle.
In meatspace SRS, you can put pictures of your memory rooms. Eventually you can even draw the objects you've created and put those drawings in SRS – along with the actual flashcards they represent! (Option: attach a random image to every flashcard, well before turning them into memory objects)
For a grace period, you practice on flashcards both on actual paper/SRS, and in mindworld.
Take care, don't create too many objects. You don't need as many flashcards as you think.
Memory objects can themselves hold memory objects. For example, in one room, you might find a Ribbing bike. On its saddle, you might find a Buddha statue. On his lap, you might find a flower. On the petals, you might find a fly. On the fly, you might find a crown. On the surface of the crown (really zoomed in), you might find a golden castle on a flat field of gold. Inside the castle, you might find a banquet. In the banquet, you will NOT find another Ribbing bike – don't reuse objects.
For true spaced repetition, try a Leitner system. Arrange your objects. Hold them, smell them – every time you handle an object. Arrange them in a system. Not necessarily numeric. Just "on that desk" is recent stuff, "upstairs on that bookshelf" is old flashcards, "in the wine cellar behind that scary vampire nest and in front of the liliputian" is some old but important stuff. Re-use things from your life. The amphitheatre, some notes on love and relationships in Momo's room, with whom you can have a conversation while you're at it. You would of course draw your imagination of Momo's room often.
Sketch, sketch, sketch. No need to sketch the memory objects in use (you can if you want), just sketch the rooms, the 'bases'.
Use emotion. Fear (the scary vampire nest) is one. A narrow bridge…
Flashcard front: Buddha
Flashcard back: Buddha with rose on his lap
Flashcard front: Rose
Flashcard back: Rose with a fly
etc.