I hope to have an option that let the input buffer be turned off, at least for offline matches; I just dislike the buffer.
Also, I would like if the game gets rebalanced in a way so that shields and grabs are very dangerous to use and it's usually better to just fight in a more traditional way. Maybe, change the shield mechanics in a way so that it's more like a parry: the shield itself is very weak, but if you release it the exact moment when you take damage, you will block the attack and shock the opponent for a few frames, getting a chance to counter the attack (not an automatic counter btw).
Other than that, I would like the implementation of more advanced physics: instead of having a fixed walking speed and running speed, it being momentum-based like in the old school platformers; instead of having fixed jump heights, make them variable depending on how long you hold the jump button; instead of having some fixed pre-coded knockback angles and strenght, make it more dynamic, much more like realistic explosion physics; etc.
I would like the wavedash to become an actual move, and get a simplified input for making it accessible at any skill level. Air dashes might be interesting too, maybe by using the same input but in air.