What needs to happen at LHR - and it will probably happen once T5 opens - is that terminals will become branded based on alliances, and any flights that are not part of an alliance will go to the "also ran" terminal.
So, we will see all "Evil Empire" (aka Star Alliance) flights leaving from one terminal, allowing easy interconnection. We will also see see all "forces of goodness and righteousness" (aka oneworld) flights leave from one or two distinct terminals, thus also allowing easy interconnections.
Everyone else will leave from what is left.
AFAIAC, this would seem to be a sensible way to operate LHR.
Dave