Jeff was certain that allowing editing during slow mode would defeat the whole purpose of slow mode, because users would edit their posts to circumvent the timer, turning the thread into a chat room.
But we’ve allowed editing in slow mode for years now, and it’s literally never happened, not even once. If it had, it would be extremely visible to anyone reading the thread.
I speculate that the abuse Jeff imagined has literally never happened on any Discourse forum anywhere at all. It’s a plausible guess, because slow mode still disables editing by default (so admins have to take an action to enable slow-mode editing), and because if it’s never ever happened to us in more than two years, it’s probably never happened to anyone.