This has been requested a number of times, most recently at http://pkp.sfu.ca/support/forum/viewtopic.php?f=2&t=4104. 

For any given file revision, allow for the ability to also add revision notes. This is already partially in place (ie., users can add commentary notes to a specific part of the workflow process), but these notes aren't tied to a specific revision. Possibly consider copying the galley upload process for any workflow process that allows for revisions: 

-- user uploads file
-- the system returns an intermediary page with file information, which also includes the option to add commentary to the file
-- clicking save on the intermediary page returns the user to the workflow page 
-- iconized links to commentary are available beside the uploaded file on the workflow page