Hmmm, a universal chat room for guilds, that would be pretty cool..? Not sure if it's possible, but it would be cool to sync main chat for all servers. I guess that kinda defeats the purpose of different servers though. Currently, Guild owners can promote temp moderators to moderate their guild server's chat. I'm not sure how Co-owners would work out especially since guild ownership can be transferred once a week now.
Interesting!
Guild chatrooms could work... but they'd probably be a little different than the format you proposed. The grouping system (i.e. member, mod, admin) on PR2 is very global in the sense that it would be hard to promote a member to something like a temp mod in just one chatroom.
Something I've wanted to do for a while is adding password-protected chatrooms; However, I'm having trouble figuring out how to balance the client's limitations with the server's ultimate power. I feel like this could be sort of a compromise. It would be a challenge (but possible) to add a chatroom that could only be accessed by members of your guild (i.e. with the name "guild").
The most difficult part of dealing with the antiquated code of the client is just figuring out how to make it do something it wasn't meant to do in the first place, without breaking things.
When it comes to chatroom-specific moderators, I don't think that will happen. Knowing myself, I'll probably look into it at some point, but it would be very difficult if possible. In the meantime, if you'd like a private chatroom which you can moderate, you can buy a private server for your guild and promote server mods with the command /mod promote *name*.
Thanks for the suggestions!