I’ve long been in the habit of holding the stirrup forward when my littles dismount for the reasons stated above. I had a girl receive a similar injury to Alterrain’s, though thankfully just resulted in a nasty scar, very close to the target though. I had never heard of it, or thought it a possibility before that happened.
Not for or against the rule, just another incident to report. I would certainly continue with peacocks at home though, any safety measure you can take, should be taken. I do think though that it’s a little odd to instigate a rule like this unless the injuries were more common than we thought.