it will fill up almost overnight by taking traffic which would otherwise stay at Gatters
I would take issue with the word "will", as a proper strategic review would ring fence a proportion of these new slots as non served domestic routes to allow connectivity within the British Isles (yes I KNOW!), to be safegaurded and built upon. That would be the likes of INV, JER, IOM, GCI and the possibility of adding MME, NQY and maintaining LBA. This would allow LHR to directly benefit the regions with one stop to the world and would be served by modern and quiet aircraft.
As for Gatters, look at the big players. Under no I would say :
flybe (unless they introduced the routes as per above)
easyJet (they might
try it and see)
Ryanair
Thomson
Thomas Cook
Monarch
Under
yes would be the likely consolidation of Virgin and long haul BA, but Aer Lingus serve LGW in their own right as do Lufthansa. We might see TAP and Air Malta consolidate at LHR but I suspect that would be it.
The new long haul troops would move to LHR, a no brainer IMHO. That's Korean, Air China and Vietnam. Hong Kong Air I suspect won't be on the route long enough to ask the question. Even if that all happened there's a fair bit of room to play with there if it's managed well. I can't believe I said that last bit with a straight face because if that were possible, well we wouldn't be here would we?