I've long preferred proportional fonts and positional tab stops like what you find in a WYSIWYG word processor. Got a tab position wrong? Drag it as appropriate or, if necessary, add a new one. In fact, during a period where I was doing far more writing than programming, in the days before code completion, I preferred my WYSIWYG word processor to my code editor. I had appropriate scripts and macros for cleaning up imported text files and to always save both native format and a text file with spaces in place of tabs. I also had different templates for different languages so that I could have custom processing for different languages. (It helps that a big part of that job was teaching people how to use word processors as far more than just electronic typewriters.)

Now, of course, the programmer's editor is an advanced tool tailored to the job, making it lunacy to even consider a word processor as code editor. Which doesn't mean that there aren't word processing concepts that might be valuable.

Nick Gravgaard has some good writing on the subject and links to a variety of resources, including to at least one proportional font designed for programming.