Oddly enough, Star Trek and homosexuality is like fire and water. It's always been something they danced around, perpetuating heterosexual relationships as the only existing and valid form. There's even a whole Wikipedia page, discussing this.
Kate Mulgrew once said in an interview:
Well, one would think that Hollywood would be more open-minded at this point, since essentially the whole town is run by the gay community. It makes very little sense if you think about it. No, Star Trek is very strangely by the book in this regard. Rick Berman, who is a very sagacious man, has been very firm about certain things. I've approached him many, many times over the years about getting a gay character on the show--one whom we could really love, not just a guest star. Y'know, we had blacks, Asians, we even had a handicapped character--and so I thought, this is now beginning to look a bit absurd. And he said, "In due time." And so, I'm suspecting that on Enterprise they will do something to this effect. I couldn't get it done on mine. And I am sorry for that.
So, as you can see, the actual (i.e. the pre-Abrams era) Star Trek doesn't touch that topic. Yes, there are a few exceptions in TNG, DS9 and even very slightly in VOY, but nothing concrete.
Since Abrams has a habit of changing Star Trek (so far for the worse, if you ask me), maybe he'll get lucky and change something for the better. But I wouldn't bet on it.
Edit: You bring up the question whether changing the Sulu in the new timline-skewed films would have an impact on the "old" Sulu we knew in TOS.
That's a tricky question, and it is difficult to even discuss without offending people (so, I hope I manage). There're several assumptions you have to take into account: Is sexual preference a genetic trait, pure choice, environmental, upbringing, ...? I've no idea, but I'm given to understand that some people take offence in some of them.
However, these theories all influence whether changing his preference in post 2009 productions would imply assertions about TOS-Sulu. For instance, if its genetic, the connection is obvious; Somebody going back in his life-time (we can assume Sulu to be about the age of Kirk, right?) wouldn't effect a change in his DNA. Similarly, if the environment theory applies, the changed conditions of his life (that were affected) could support a change of preference.
So, featuring any indication of Sulu's sexuality in new films without careful consideration could lead to drastic continuity errors that would imply statements about LGBT that the producers are (if they are the slightest considerate) not going to be willing to make.