More importantly, does anybody know how many galleries will be installed? I'd hope that the News Channel has it's own separate gallery which isn't taken over when the nationals are using it's studio so that they can do their own thing regardless.
As I think I mentioned somewhere (quite possibly elsewhere in this thread), if you're building a modern studio complex, you probably wouldn't tie a particular studio floor to a particular gallery.
Take BBC Scotland, for example -
Studio C's gallery will run Reporting Scotland at 1830 (from Studio C's floor), then it'll handle An La (using the studio in Inverness) at 2000. There's a smaller gallery around the corner, the Bulletin Control Room, which will then do the 2000 BBC One bulletin, from a CSO position in Studio C - though they also use it to direct the shorter bulletins from the main floor.
Besides, while they've decided how many studios they're going to build in BH, I think you're a bit early to be speculating about how they'll be used. I wouldn't be surprised if the high-ups in BBC News don't know; haven't decided; or change their mind several times before the building goes on air.