I'm an RO of the Python SO chatroom, so this is coming from the perspective of a large, active, and actively moderated room.
We have a lot of trouble getting new or misbehaving users to read the rules linked in the description of our room. When this happens, we end up having to post messages in response to the user's behavior, interrupting existing conversation flow for an uninteresting aside about rules.
Similar to the new popup that appears to first time chat users, it would be useful to show a customizable message to new users in a specific room. An additional, but not required, feature would be to disable the message textbox until they have clicked the "I understand" button, as extra emphasis that they actually acknowledged the message. The popup should appear again when a user re-enters after being kicked, to remind them again of the rules and why they were kicked.
This could be as simple as a reiteration of the description, or could be a separate message, but should require that an RO enable it for a room.
One objection is that adding another message doesn't actually make the user read it, but since we're now showing a popup to new users in addition to the help link at the bottom that's always been there, this doesn't seem unreasonable in that regard.
Another objection is that we would end up having to respond to their behavior anyway if they don't actually read the popup. From my observations, a quick message pointing a user to our rules is generally sufficient, so this would still be successful in the majority of normal cases where the user is just uniformed, not willfully disruptive.
I am not suggesting that we change the one time popup about general chat guidelines. Nor am I suggesting that the message is to communicate with users handling flags. This would be a separate message specific to each room that chooses to use it.
