I assume United is targeting O&D traffic here? 7:30pm arrival in BOS sounds rough for connecting passengers. I guess there aren't that many UA connecting options in BOS anyways and, even if they exist, they go to UA hubs already with London service.
Good strengthening of *A presence though, would probably provide a good option in addition to LH and LX across the pond (i.e. for those who don't want to fly to Central Europe just to get to the UK.)