i too would love to see these kinds of features built-in to coda docs - but coda’s power lies in it’s ability to add functionality to documents.
my clients are in regulated industries where strict document management practices are required for certain kinds of collaborative documents, even the specifications we use for developing formulas and buttons in spreadsheets and coda docs themselves!
regulators like the FAA, FDA, SEC, GAP, … etc. require auditable controls on certain classes of documents.
so we developed a “controlled document template” for these. it uses a table to record who and when the following things occured (and the reasons for the changes)…
- create a new page or section
- check-out a page for editing (marks page as such)
- check-in modified page
- delete page or section
- sign-off approval for a page
- mark a page as ready for approval, listing approver roles required
it places buttons on every new page to be used to trigger these procedures and will ‘highlight’ any page that does not use the right procedure.
comments are also used for collaboration, but they are always cobsidered ‘outside’ the document. like post-it notes - useful, but not binding.
the template depends on users following the procedures. so it could be circumvented on purpose or by accident. but in a controlled environment, nobody would dream of committing such a crime 
and it can be set to record the text of each page for these events - so even the strictest auditors are happy with it.
and, of course, further functionality can be added - that’s the magic of using coda!
the template was developed under contract so i must check with some folks before i can publish it here. which must await the resumption of work after this holiday break.
edit
i should point out, in case anyone is interested (shamless commercial plug), that we are extending this “controlled document” capability to the blockchain. a pack that will turn the final, approved, signed-off, document into an “NFT” on the Ethereum blockchain. but i wont be publishing that code here
max