WATABENCH
I can't see BRS-Florida being a viable regular scheduled route, leaving aside any runway question.
A weekly charter flight certainly, perhaps more than one: other regional airports of the same size, and some much smaller, have charter flights to Florida as well as to Toronto so, to a punter like me with a layman's interest in civil aviation, the sticking point can only be the dreaded R.
As for more scheduled transatlantic routes (to destinations more promising for the genre than Florida), let's hope the CO service to EWR will succeed and convince some hearts and minds in the airlines.
I think hearts and minds of some pax still have to be won over though. In the past week or so I have spoken to three groups of people in the Bristol area who are flying to New York later this year at different times, and who are all flying from LHR to JFK.
They were all aware of the BRS-EWR route but told me that their travel agents got them much better fares from LHR. One lot travel frequently from BRS around Europe and would loved to have used the EWR route but money obviously talks.
I fear that LHR's proximity to Bristol will always attract a significant number of pax who might otherwise have used BRS. Apart from BHX, there is no other regional airport of any size closer to LHR than BRS, and of course BHX has a far more populous catchment area than BRS so is in a stronger position to 'stand up to' Heathrow.