I've started using the builtin "println" function for stdout debugging to get around the Damnable Use Requirement. It works without any packages imported, so that the very low-level stuff can tell it's alive without a full stdio library stack in place.
I don't want to commit temporary debug cruft to version control, so I'd still need to keep adding and removing that whenever I do a commit. Though I guess I could just always skip it with git add --patch.
I do have need for some solution, since I have packages that don't do anything with strings and therefore don't import fmt, but which still get bugs which I need to debug with the stdout.
One more robust approach would be to fit a complete configurable logging system permanently in place.