I am pleased for BA this should be a good move. I must admit I like the check area in the North Terminal, with the quick access to the slow fast track line. From memory this has not been open that long and still appears fir for purpose. But as it has already been said its quiet a hike from the rail station to the north terminal for joining passsengers.
I work in Westminster and its much quicker for me to travel to Gatwick than Healthrow the caveat being if you can across to Paddington quickly and join what appears to me as one of the worlds most expensive train journeys when considering the cost per mile.
All we need now is some investiment from BA in terms of route coverage at Gatwick.