This is one of those issues that make me scratch my head in puzzlement. Windows supports UTF8 fine, and has done for decades. It would be hard to find a text editor that does not support UTF8. I think that argument is bogus. I don't know about IPC-D-356 etc, I don't have access to the specs.
If it was my code I would let the user decide with a save option, and/or be adaptive when saving the file - if there are non-ascii characters save with UTF8 encoding, else save in 7 bit ASCII
Of course it would be bad to always save files as UTF8 and potentially screw up everyone using ancient CAM software, but always saving in UTF8 is an obviously bad implementation so I don't why any programmer would assume that is the proposal.