Note for Pau -- let's discuss this and figure out a UI.
After editing any existing content, when the I click "Save", it should give me a dialog requesting an edit-summary.
cf. discussion at https://www.mediawiki.org/wiki/Topic:Sedsjclychk64ngk
Copy from merged duplicate:
As a user, I want to be able to provide an edit summary when editing other people's comments, so that it is clear for any one why I edited their replies.
This is possible on normal (wiki) talk pages, and is not possible on Flow talk pages. Therefore, users just give up doing constructive edits to existing comments. E.g. from Portuguese Wikipedia: