I am always intrigued by new SRS systems, though sadly most are just "simplified" Anki clones. I have always been tempted to throw my hat into the ring.

The biggest area for improvement is probably deck collaboration. Most SRS proponents often state that its bets to make cards yourself because the act of making the cards is a key part of the learning process. I don't disagree, but part of the reason that making cards your self is recommended is because the shared decks are, on average, terrible.

After that I would like to see more built in support for non front/back or cloze cards. There are a lot of other card types that you can make, but are difficult or impractical to do in anki. Things like "slow" cards, one sided cards, code/music/math/text cards. These can all be done in anki, but it's a pain.

Then support for card order/hierarchy/prerequisite an and encompassing graphs like what MathAcademy does.

And lastly, a web first experience. Anki is offline/local first. That has the benefit that you are always safe from being rug pulled. But there are a lot of places (like work) where local first does not work well.