If you have the Replay add on, I think you should have the ability to send "share via Replay" links from a file in dropbox. When using this option the file would be available in Replay automatically and sync with that file in dropbox for comments/changes. Versions could be uploaded into the same folder with a naming scheme. Bottom line, everything should be do-able within the dropbox app - everything from setting up folders, workspaces, versions, etc... leaving replay for the viewer experience, comments, and other forms of communication about the file. All file upload/download/versions/links should be integrated into Dropbox, so that file management can be done from the Dropbox side