Multi-window chat is in testing. I hope to have great news regarding rollout to the public rings soon.
We are working to ensure that multi-window and other future multi-window experiences are of the highest quality when they release.
Thanks!Tory Graf commented
I agree. This really is needed. The navigation back to a chat is really cumbersome and wastes time. I want to be able to quickly get back to my chats without having to back out of whatever I am working on.