This is a complicated subject.
One of the advantages of Fountain being a plaintext format is that we can leverage the many robust existing Unix tools for working with text files. One type of these is a version control system (VCS). VCS allows authors to keep the entire history of changes to one or more text files. There are many version control systems but the most widely used is Git which forms the basis of GitHub.
Emacs has a fantastic in-built facility called Version Control (or VC) to interface with a host of version control backends.
Fountain Mode currently has no specific way to handle revisions.