No doubt that AO-91 and AO-92 may not be the best choice due to the extreme popularity there, but perhaps AO-27 or SO-50 could be a good option. Or maybe even PO-101.
I would think that if AMSAT is setting the rules (or guidelines), then it should be AMSAT that hosts the event. Therefore I would suggest that ONLY AO-91 and AO-92 be considered. As for getting the word out, I think most of us will listen to a control operator who states "HT use only until XX:XX UTC" (along with a proper callsign ID, of course). There are always those knuckleheads who try to make QSOs against the control operator's wishes, but I'm sure "cancel culture" will take care of them..... (whether or not it's justified is another topic of discussion).
Remember experimenter's wednesday? Maybe "experimenter's every-other wednesday"....