Norwegian - Judging by the fact that their fares are only a little below BA/Virgin currently I'd say they are probably selling well, although please do not quote me on this. I cannot see why they wouldn't be, as Norwegian offer a good product and price, and more importantly they have only launched the flights with quite low frequencies. This technique seems to have worked rather well on their med routes launched last year, so it would be nice to see lightening strike twice!
As for BA it was rumoured that the 12 787-10's on order were destined to replace the LGW based 772's. This would be an increase of ~2 aircraft compared to the current fleet, plus I'd imagine there might be a few more seats on each of these. What would happen with the 4 class routes I'm not sure, to have mixed configurations in a fleet of 12 seems a little impractical. I'd imagine the most likely solution would be to also have a couple of 4 class 789's for BGI/BDA and any other routes that may have some demand for first in the future.