Upon trying to submit an edit, I got a red message box saying
Your post cannot be submitted at this time due to the volume of spam and abuse originating from your network. We apologize for any inconvenience. See the help center for more.
Then I realized that I was trying to submit it anonymously, from a Tor session. Not a surprise, Tor users are used to those hindrances, but that is not my point.
That box should show up as soon as the edit button is clicked, not only after the person has already worked on the edit and is about to submit it (because it is obviously an avoidable waste of time).