Interesting. They've basically already had this district with the 7x, 8x cars covering this area for a few years, but the cars were still technically part of District 6 still. My guess is it's busy enough to now need it's own staffing/funding.
I wouldn't be surprised if the channel assignments stay the same. Most likely it's still part of the East Command so it will stay on whatever channel District 6 goes to (SP 3, 4 or 6 depending on which part of the day/staffing).
7A and 7B used to be part of District 3 many years ago.