Okay, so as much as I would've liked for this to "come out" naturally on the show and not spoiled by the BBC publicity machine two weeks before airdate, I am pleased to see some real diversity in the companion role, yet I'm hoping that Bill's sexuality won't be THE defining characteristic. Steven Moffat created the character, so I have my worries. A lot of fans are expressing relief that there will be no romantic interests between the Doctor and Bill, but I will add that it will be a sure thing that Moffat will not pull the old "kill off the gay/minority" trope for fear of pissing off what's left of his fanbase on his way out the door.
Or will he?...
The Mary Sue's article seems to imply that Bill will be continuing when Chibnall takes over, but I have heard no other word about her staying on after Capaldi and Moffat leaves. But if she does stay, and the next regeneration of the Doctor is female, and the writers made Bill gay so that she will have a romantic interest with a female Doctor, I'm getting off the bus.