Correct me if I'm wrong, but aren't the 787's US based? So the 787 and crew would technically be based in, say, Oakland, and operate to EDI, where they overnight?
Therefore there is no reason why we couldn't end up with both a MAX base and a couple of 787 flights. But given how far ahead they have announced Manchester, I guess a summer start for East Coast with the MAX will come first, with possible 787 flights coming either Winter 2017 or Summer 2018.