Navpi
Interesting theories but any new runway at Heathrow (or little old Gatwick) is going to take years to bring into use so:-
1. Will Easyjet (or RYR even) still be around by then?
2. Even BAW may not be as we know it , maybe IAG will be a feeder for QATAR AW by then
3. Brexit effect
4. Trump may have killed us by then!
Suggest we wait and speculate more accurately in 5 years time when the cement is ordered and the "anti-brigade" have been placated.
The world and aviation change too quickly for accurate predictions.