The reason AST editors look a lot like lisp is because lisp pretty much is just an AST. There's no technical reason the AST can't be a more complicated structure than a list, and you can present the AST any way you want - you don't have to show parenthesis. You can use mathematical symbols, whitespace, images, fonts...

The problem is the further away you go from lists of symbols, the more complicated the AST is to edit and to present to the user, and the more complicated the interface is for the user. It's not an insurmountable problem though.