It's been over a year, can you please ask someone at backblaze to add a single line of code into the snapshots so you can leave a comment? Right now if you make a snapshot, the only info is the date and time. Not the data, what's in the snapshot, literally anything about it. Please!
Actually, very very quietly as part of the 6.0 release (4 days ago), we now allow you to "name your snapshot".
While this is not a comment, and you can't change the name LATER (so useless to old snapshots), at least going forward you can put up to about 1,000 characters of description in the snapshot name.