I don't watch the show but re. fandom: it hates Moffat and thinks everything in the show is done either because of his sexism, his contempt for the fans or because he's shit at writing. I have not yet worked out how Gatiss figures into this.

Unless the show is going to definitely end for ever then I very much doubt they will even be *allowed* by TPTB to put Sherlock and John together. This is based on various problems there have been with getting various things done on Doctor Who. Sherlock sells massively all around the world so the BBC are likely to be pretty conservative about it.