This might seem like a ridiculous ask, but after getting used to composing TeX in Overleaf and TexPad, both of which can show a preview of the compiled code in real time, it doesn't seem like it would be too difficult for an editor to allow editing directly in the output. The output pane would basically work as a GUI that allows you to you edit the source more naturally, like in a traditional word processor.
For mathematical formulas and complicated formatting commands, you'd just go back to the source. But for basic text (which is 90% of most documents), the ability to type/highlight/copy/paste right in the output would be a much nicer experience. Does any editor allow this?