Enough about the second city stuff!
Now, Glasgow's runway is 2650m long, 51m longer than BHX's and yet they can handle a 747. I'm not comparing the two.
Also, there are concerns that Etihad cannot be at BHX due to the fact it's too close to MAN and LHR, but they operate into LGW with no problems.
About AI, there have been discussions going on about a relaunch, and I would prefer more than 6 flights a week. If it was more profitable than the LHR-India route then it's stupid to worry about slot protection, as they have enough airlines already, and enough Air India flights. Seems the furthest you can get with a 777 from BHX is India.
Now PIA, they have a codeshare with Turkish coming up, and they would be expanding their UK routes. I would hope that expansion should be made on the BHX and LBA routes, as I think the MAN and LHR routes are large enough.