A new United Polaris lounge is under construction at Dulles. The shell of the building appears mostly complete, so we are likely looking at six-nine months or so before that opens.

Given the number of international services at Dulles and the high standard of every other Polaris lounge, I expect this one to be very good and likely outshine the BA IAD lounge. (Granted, you need to be in business to get into a Polaris lounge, so not exactly apples-to-apples).