Criticising the referees has always been a no, no. Although the coaches have managed to work around it.
It sounds like now they can't even talk about the officials.
I am not sure how long this will last. Most of the coaches don't have anything else to talk about when they lose. There are going to be controversial decisions that people are going to discuss.
Overall the behaviour on the field is a lot better than 10 years ago when players would rush the referee on nearly every decision. The edict that only captains talk to the referee is a lot better.
I'd like to see the time between the decision and captain's challenge be ruled a bit stricter. Some of them seem to take a lot longer than what was proposed when the rule was first brought in.