As it stands the proposed deal is very good for the USA but much less so for Europe and the UK.
The USA gain rights to fly worldwide out of the UK and Europe and in theory Europe and the UK gain the rights to do the same ex USA. The potential value to the USA would however be far greater than for the Europeans. For example a US carries could operate to anywhere in the world out of London, giving a mix of short and long haul possibilities. Where would a European carrier go out of the USA? S America, Transpacific and Canada are the 3 possibilities and none of them very attractive in terms of either investment required ( transpacific) or markets ( S America and Canada).
Also , whereas the USA could start services ex UK to all those places it already has open skies deals with already ( eg a number of Far Eastern countries) immediately, the UK/Europe would have to negotiate new open skies bilaterals with any countries they wanted to serve ex USA. To gain these it would have to grant open skies to, for example, all the Far Easterns ex UK/Europe, so UK would face prospect of these operating worldwide ex UK. Fancy the idea of high quality/ excellent service/lower cost oriental carriers on across the Atlantic? Great for the customers but a real headache for the Europeans.
Think about it....................................