The Back Room has the same qualifications as the Balancing Team. If you want to get in, you apply to join the Balancing Team and get accepted to both, unless you specify in your application that you only want to be in the Back Room. Inactive Balancers lose access to Balancing but stay in the Back Room. Applying to the team is the only way in.
We don't need a new back room, we just need the current one to either be active in both balancing and back room, or wait until balancing for 0.9.1 simmers down. The back room will probably be active once 0.9.1 releases.