I would like them to abandon the environmental hazards and items.
They were cool at first, and they are a neat idea, but I feel like the game has suffered a lot because of them.
Specifically the whole walk speed, stages being too big, huge distance between characters, this all feels like a product of the environmental hazards.
Stages have to be very big to accommodate all the items scattered around the stage, and the characters have to be smaller and farther apart so you can actually use the items and see them. If the camera was too zoomed in, the stuff would be vary hard to see and be able to react to.
Or the other option is too keep them and just make the game crazier, everyone faster, dash cancels, everyone has an air dash, super fast mobility, like a Marvel game, and have the hazards just be combo extensions.