Assuming the agreement gets past the EU Council (v. likely) and the US Congress (...), the most likely opportunities would seem to be:
Continental, Delta etc could access Heathrow - but they would have a hell of a job amassing enough slots to make it viable.
BMI could fly to the US from LHR.
Virgin might find it easier going running a franchise operation in the US.
BA and American could gain anti-trust immunity to allow them to cooperate more closely
Lufthansa could operate transatlantics from 'their' Zurich hub.
Several opportunities would open up for Aer Lingus
Hopefully European airlines will all make a bit of money, but probably not much, carrying US government business which up to now has been closed to them.
Talk of locos between the UK and the US is nonsense, there would never have been any obstacle in the first place. The current UK/US bilateral is flexible enough, and the two sides liberal enough, to allow just about anything as long as it doesn't involve Heathrow, and to a lesser extent Gatwick.