Code is not a visual thing nor does it even represent a visual thing -- making it visual accomplishes nothing (except for making it visual).
Pictures, formatted document text, 3d models and videos are visual things. Music notes are a specific type of visual language, audio is time-linear-spatial (or something less gibberishy like that) and can be represented visually. These things are all extremely different from software.
But what we are really missing is execution visualization. Applications aren't code, applications are execution systems and it's a shame to test execution/debug like we do today.
As someone has said, it's almost impossible to test all inputs for an algorithm, it's impossible to prove the correctness of an application without testing it.
Without testing we're nothing, most of us can surely say in which conditions our applications will break, but how sure are we to say in which conditions will it work? Much harder.
I would love to work in IDE improvement as I believe there is really a lot of things to improve.