Exciting though a free-for-all race would be, ATC know before an aircraft pushes back what its position in the takeoff sequence should be and direct its taxy route accordingly.
Having said that, I have it on good authority that Heathrow went to see McLaren at Woking a couple of years ago to have a look at the technology the F1 teams all use to schedule their pitstops efficiently so that cars can be slotted back into the sequence in the optimum position.
Sadly the rumours that the LHR taxiways are to be widened, with DRS zones, to make overtaking easier probably aren't true.
