BHX is not as well placed as MAN for domestic hubbing and does not have services to NWI, NQY, EXT and SOU which I am assuming BE are hoping to feed via MAN into ABZ, BHD, GLA and INV (and vice versa). I am also sure that BE codeshare with EY so another incentive to set up a hub at MAN to feed this flight.
T2 was designed for hubbing but for connections from GLA, EDI, ABZ and BFS via BHX into the European cities that BA then served from BHX (and that at the time weren't available as non stop flights from the aforementioned airports) hence the name Eurohub - there was no advertised domestic hubbing as far as I can remember altho it was probably perfectly possible to buy a BFS-EDI or GLA ticket travelling via BHX......does anyone know if BE gets much feed into its European flights from GLA, EDI and BFS via BHX - perhaps this is something they might look at although most BE destinations from BHX are served direct from these airports by other airlines nowadays