I see nothing wrong with this proposal because it allows organizers to decide whether or not to implement the move limit. I imagine most competitions would not use it.
I understand that move limits do nothing to change how long the event actually takes, but it does affect how many staff hours are required to check the solutions. People here have been saying "just get some trusted competitors to help out", but that may not always be possible. Maybe all the most trusted staff are busy scrambling/judging elsewhere during the competition, and checking FMC solutions is really the only thing that can be put off. Such a situation may not be that common, but that's the reason we'd leave it to organizers to make the call, since they're the ones who know the schedule best.
Perhaps I can offer a compromise that I don't think has been mentioned (it's a long thread, so sorry if it has). Maybe for competitions offering multiple attempts, you can implement a "soft cutoff" equivalent, where the first attempt must be under a certain number of moves for the next attempts. I imagine the burden on staff can be pretty high if every competitor suddenly wants a mean. A soft cutoff reduces this burden for the second two attempts, and might allow more competitions to offer the opportunity at a mean.