In Sphere, I would think the MOST common use case for a wave file comment is to open/create what you might think of as an issue (similar to software "issue trackers").
So for example: "I think the guitar is too loud here?" is a sorta issue with the mix.
It would be nice to have comment threads have an addition element (or two) indicating whether the comment IS an issue, and whether the issue has (since) been addressed. Then it would be nice to be able to FILTER the comments so I can only see "unresolved" issues.