Maybe its just a PR stunt, or pandering, but I don't really get why someone's sexuality is even all that important unless its relevant to the plot.
I can honestly say I've never thought about Sulu, or Chekov's, or Scotty, or Bones' sexuality as it hasn't been all that relevant. Maybe I'm forgetting an episode or two from the '60s, or a scene from one of the movies, but for the most part the only main characters that seemed to have any sexuality as part of their core character were Kirk, Uhura, and Spock.
If Sulu has a kid that is at risk in the new movie and its relevant to the plot, fine. But why should it matter if he is hetero, homo, bi, or asexual. And if the kid was born in a hetero relationship, born through a surrogate mother (in any kind of relationship), or adopted in to any kind of family.
Why should it matter???
I'm sure people would argue that gay people need to seen as role models in movies to feel accepted in society, etc, but where does it stop? Do we need all sub-segments of society represented in blockbuster films?
I've probably answered my own question as I'm guessing this is just PR or pandering. They should have just left Sulu be an Asian dude that pilots a starship without having his sexuality be part of the discussion.