Fun fact: George Takei himself complained that Sulu is portrait gay in the new movies. He said that even tho he himself is gay, he always played Sulu as a straight guy. But why would the headcanon of an actor be more important than any other
I mean, if it informs the performance meaningfully, it's part of the end product. Doesn't mean it's necessarily canon or whatever, but it certainly has the potential to impact later performances if direction moves away from the actor's previous internal preparation.
I could see it being off-putting to work under a director or with writing that bleeds your public personality into your role, especially if it's one you've gotten to a certain place with.
Like even as a roleplayer, any character i might embody in the moment has a life of its own that's distinct from mine, and would make decisions that I wouldn't. If someone tried to push me into acting a way that's more typical of myself out of character or that's more in line with a different character I play, or if they reacted to the character based on that outside stuff, I'd certainly resist it.
True, I totally see your point. I think there are different ways to see this:
First, it's someone else who played it so he wasn't forced to do anything. It's just a role he played and now someone else does with different interpretations. You wouldn't blame a Hamlett actor for performing differently than their predecessor. Sure, it's different since Sulu was brought into existence by Takei and didn't really exist in a book or something but still a fictional character played by different people.
Since it's just one little scene I didn't even remember after the first time watching, it isn't part of his story or character building or something. He is just greeted by his husband (or partner) and daughter. In my eyes more of a homage or easter egg to Takei than forcing his personality into the character.
Lastly, HolLyWood goNe w0ke aNywAyS. I don't mean this negatively obviously. Media puts diversity into more and more places and it doesn't even have to do with Takei himself.
Even tho I started the last paragraph with lastly, let me add that I think it might even have more to do with losing control of your creation. Sure, Sulu started as the character played by Sulu but he developed further. It's like trying to force the genie back into the bottle. Sulu isn't Takei and Takei isn't entitled to control Sulu.
To be fair, John Cho played Sulu straight until it was revealed that he was gay. And even then, there wasn't much gayness to his acting. Unless you count bringing a sword to a skydiving phaser fight, but I'd consider that more bad ass than gay.
It's not just how Takei played it, the first thing an inhibition-free Zulu does in The Naked Time is to go after Uhura - and Mirror Zulu obviously has the hots for her too.
This is wishful thinking. It was made within a heteronormative society, and most characters who have love interests and relationship histories are hence straight.
Unless stated or shown it's far more of a head cannon to assume a queer identity where none is suggested.
No media can fully escape the culture, period, and context it was created in.