LHR will see a benefit though - bmi can open the market from their view point and increase competition and more than likely reduce fares like it did in Europe, and like it has done on the London, India route. Slots can't be given by a government as they are controlled by the airport/slot people - so airlines will have to wait or buy from an airline, just like Virgin/Qantas did when they bought slots from flybe.
Delta have already acknowledged this and said that they will queue up for slots but will probably be a couple of years before they can start LHR - but until LHR even gets opened up they can't wait around.
The only way more slots will be given up is if a joint venture type agreement goes ahead between say AA and BA - at which point they would have to surrender some slots for competition rules. Or wait until LHR finds more slots maybe through mixed mode operations, or a future new runway???
But you also have to think that European airlines can now also start LHR to the US if this goes through - yes DL may not be able to get any slots, but why couldn't KL or AF operate LHR-ATL with DL codesharing?? LH may also want to start new services from LHR - they won't get the feed they need (although they will have STAR feed still just like bmi would) and could still start a service to a STAR hub like ORD, IAD etc - unless they fancy increasing their presence in New York for example with flights from Germany and the UK - a good offering!!! Just like Virgin could open up AMS-NYC, CDG-LAX etc focusing on their point to point traffic like LGW etc!!
So the UK consumer will get a lot of good out of this, there will be increased competition on the LON-US markets, markets like Las Vegas, Dallas and Orlando would be opened up from LHR (at the moment they are restricted as only certain amount of markets can be served from LHR, even for the 4 airlines allowed access).
And it isn't just LHR that gets included as the US cargo carriers like Fed Ex will be able to fly fifths beyond LHR to European points (eg LON-AMS)
So a lot in this for everyone, but the consumer more than anything - so why shouldn't this be a good direction??? And it may start changing the face of the US aviation map which to be honest needs a kick up the rear end!!