I thought this was up for the AGM, not that the decsion was already made and announced here before I remember reading in Yowl.
I was a member of a forum that did this previously and two things happened:
1. All non members asked for their posts to be removed from all active and archive threads being that they were posted before the rules were changed
2. A load of people left and eventually the forum was a shell of its previous form
I don’t remember the membership being offered a vote on this or even it being proposed or open for formal written feedback for a time before a decision was made. It just seems a terribly retrograde step to me.