This has been implemented now. The short story is: room owners can kick abusive users, who will then be banned from re-entering the room for a certain time.
Of course you want not just the short story but all the dirty details, so here they are:
In the user popup that appears when you click on an avatar in the "who's here" list or next to a chat message, room owners have a new action available:
We chose the name "kick-mute" mainly to clarify that this is different from the old "kick this user" (which was only available to moderators, and, as you noted, was fairly useless). We just say "kick" everywhere else.
Room owners may have to reload the page to see this new menu item.
Clicking this item and confirming an alert saying
Do you want to kick [Name] out of this room? A high number of kicks may be reported to moderators.
will, well, kick the user. They will drop out of the "who's here" list, and they will be redirected to a page that (almost precisely) contains the message that Shog9 suggested. They will also be shown this page if they try to re-enter the room.*
The kicking room owner will be informed how long the kickee will have to wait before re-joining the room (see the section "Ban duration").
*If the kickee has loaded the current chat page before this change came into effect, they may be redirected directly to the rooms list instead, so they'll have to try re-entering before they see this message.
Who can be kicked?
A room owner can kick any user (including other room owners) from their room, provided all of the following are true:
- The kickee has spoken in this room within the last 24 hours.
- If the kickee has previously been kicked from this room, they have spoken again after said ban was over.
- The kickee is not suspended.
- The kickee is not already kick-banned from this room (this also pretty much follows from 2.)
- The kickee is not a moderator.
The kickee does not have to be in the room at the time they're being kicked (requiring this would allow trolls to prevent being banned by entering a room, quickly saying "TABS ARE BETTER THAN SPACES!!!!one", and immediately leaving the room again before anyone could have taken action).
If this is the first time the user is kicked anywhere (i.e., not necessarily in the same room) in the last 24 hours, the ban will last one minute. If it is the second time, the ban will last five minutes.
If it is the third or more time the user has been kicked within 24 hours, the ban will last for 30 minutes. In addition, the user is automatically banned from creating new rooms and from sending invites. This automatic ban does not expire and can only be removed by a moderator. Moderators can also remove the kick-ban before it expires.
If a kick action fulfills any of the following criteria, an automatic moderator flag will be raised (on the kickee's last message):
This was at least the third time that this particular user has been kicked within 24 hours (this is the same criterion as for the invitation/room creation ban, so moderators can immediately evaluate whether this defensive ban is unnecessary, appropriate, or not even enough).
This was the 3rd, 6th, 9th, etc. time that this particular room owner has kicked a user within the last 24 hours.
This was the 5th, 10th, 15th, etc. time that a user was kicked out of this particular room within the last 24 hours.
The automatic flag will contain the numbers for all of these values (number of kicks against this user, number of kicks by this room owner, number of kicks in this room) that cross the minimal threshold (3, 3, or 5, respectively), and a link to a page that shows the details on the kickee's current and previous bans, and that also lets them remove the bans.
If a kick action caused an auto-flag, the kicking room owner will be informed of this fact.