Looks good!
It seems one trade-off you made in your structural editor is to forgo conventional math notation in order to keep the shortcut access consistent. Does it feel painful to not be able to just dive in and just type the text you need? I mean, what you have is awesome for exploration, but what about when you kinda know what you want and you just want to type away at it? Does that feel... laggy (for a lack of a better term) to use the structural shortcuts?