Format to personal style on open. Format to project style on save. The project style is then consistent, but irrelevant.

This sounds good and might work for programmers who are working in well-established languages with mature tooling.

For me, I’m opening so many kinds of text files, I’d need a parade of parsers and pretty-printers to pull it off. I can’t see it being a realistic option in the near term.

Same here. In a given week, I’ve opened files across 6 different {programming} languages

I have tried this but the formater in Eclipse messes up too many edgecases or nicely column aligned struct definitions to make it work for me.