Dreamweaver used to do this for HTML, sometime before it got bought by Adobe. Today Dreamweaver seems like it would be usable on a 90 THz computer but I can do 10 push ups waiting for the UI to settle down after typing "Hello World".
A split-screen SVG editor would be particularly good, since so much of editing an SVG file is getting the numbers right. You'd face many interesting problems, such as exposing decimal math to the user (whatever iffy floating point is used, your git commits are going to be awful unless you "snap to grid" in factors of 1/2 and 1/5.)
What I'd particularly like to do is have control of the structure of the document so I can group elements with the discipline of a programmer.
A tool like that still might not be satisfying because Bézier curves were made to make people feel like they were bad at computer graphics and took over instead of better alternatives that were patented at the time. I was shocked to find that my favorite character designers don't know how to draw anime characters with Bézier curves.