Thanks for the summary of Bermuda II, B747-437B. Based on what you say, there is no way BA is allowed to operate nonstops to PHX, SAN and DEN from LHR. And yet that is what they have announced they will be doing from October!
There must have been a renegotiation of the Treaty, or else BA are incredibly certain of getting it.
I agree that slots are a big problem even if DL gets access at LHR. BA has spent very large amounts of money buying slots from SN (7 per day) after it went bust and also from a number of smaller European airlines (who it has given LGW slots to).