Whatever the performance requirements or route potential of any aircraft / config I believe at minimum BRS requires a starter extension. TORA is limiting any decisions. I know many who in a heartbeat would choose to fly out of BRS and pay a small premium to avoid LHR, myself included. I know the 'build and they shall come' is not generally a sensible way to approach these matters and appreciate the airports caution but is it more to do with the local politics that could come into play with any runway changes?
On a separate point, stands are a bit limiting. I assume old staff car park could help but perhaps not by enough. Long haul AC are space guzzlers?