Originally Posted by Blumie

That's a very interesting point that I had not considered. I imagine, though, that there will still be many travelers connecting from other carriers onto BA (I, for one, will continue to fly AA from the US to LHR and BA onward, allowing me to experience the "swanky" new terminal and the "Galleries" lounge), but hopefully your expectation will hold true and T3-T5 connections will be relatively painless.