I have a thought about the "masterplan" which I would only ever share annonymously.
If HS2 and the Birmingham Interchange do happen as planned it is predicted that the journey time to London Euston may fall to as little as 38 minutes. This would make BHX an attractive option for some people travelling to central London, and BHX would, in a way, become one of London's airports.
The airport and the city and the region would then have two options, either to market that new connectivity in some way, or to continue to market BHX solely as a gateway for Birmingham and the midlands region.