Some people are mixing up the following concepts:
1. Is there enough "onscreen" evidence to definitively prove Sulu was gay, straight, etc.?
2. Is it a good idea to retroactively make Sulu gay the whole time?
3. If so, do original creators and actors have the ability to prevent this change from happening?
...and the unrelated, in my opinion, question...
4. Was the original Sulu straight, based on the totality of the evidence in front of us?
This last question is the one I am most interested in, mostly because I think people here are having a hard time separating out concepts 1, 2, and 3 from their answer to 4.
We have a decent amount of evidence that old Sulu was straight, and zero evidence that he was gay. Put all of that on the scales of justice, and see which way it tips. (The answer is "straight," by the way.)
If you have come to any other conclusion, it is because you are mixing your thoughts and feelings on 1, 2, and 3 into your answer to 4.
I agree that is it is a good time to make new Sulu gay, and that the Kelvin, wishful thinking, magic, or creative license is good enough reason to make it so.
The original creators and actors don't have the ability to prevent new Sulu from being gay, nor do the new creators and actors have the ability to make the old Sulu gay.
Canon, onscreen evidence, personal experience, the sign of the times, and well-written posts by writers/actors all factor in to the stew that causes each fan to believe what they want to believe, and once locked in, that fan is sure they are right. We choose the pieces we like and discard those we don't.
If you like the idea of new Sulu's becoming gay as of Pegg's recent pen strokes somehow re-writing 50 years of history, retroactively, no one can stop you. But you are acting on sentiment, not logic.
From a purely logical standpoint, old Sulu is straight and new Sulu is gay.