Feel like its so simple and easy to implement that its just pointless to not have in, I think it would prevent many false reports but more importantly help the admins get to the reports faster having, seperate tabs open directly to the players involved in the reports to get the story straight. Think its pretty simple but would be just a plus to the already great features the server has.
Staff can open one if needed, an always open chat would just create a venue for harassment/unneeded talk
Also as wink said, it's already a thing. If staff feel the need to we can open a chat between the two parties and us.
