It would be great if mp3tag had support for the PSF (Portable Sound Format) tag format. The format has been around for a while, and currently, there is no tagging application capable of editing these tags beyond an old command line application. These tags are most often used in *.mini?sf and *.?sf files.
One thing not mentioned in this specification is that the tag is simply appended to the end of a file and begins with [TAG].
I hope to see support for this format implemented in mp3tag.