I already do support it, though I don't support "Token gays". When I say this I mean they can't just be in the game just to tick the boxes of the gay character being in there. The character must be a part of the story, must serve a part of the narrative and structure, not just a throwaway.
More gay characters with purpose please, make sure they're on equal footing with the other characters, some more positive stories or stories that don't just dwell too far on their sexuality if it is unnecessary.
Bi representation is fine also, but once again make sure they aren't throwaway or 2 dimensional.
I mean, lots of types of characters are in games just to tick boxes. There's, by default, often a main boy (sometimes a handsome space marine) and a female love interest. Do these need to be justified? My understanding is FE used to have more male than female characters but equalized the numbers more for the purposes of romance. I'm sure these romances are of variable quality and importance but I just want... the same thing straight gamers never have to worry about getting.
In a cast as large as FE3H's, lots of characters are going to be, or strike some, as two-dimensional but people are going to care about them regardless. I don't begrudge straight people their horny dating-sim lite elements in games, I just wish I could participate in the fun, too. Loved Stardew Valley, where everyone was bi. It made that game more fun and accessible to me, and was one of many highly unrealistic elements crafted to give players a good time. Also Dragon Age II, but I don't think four-five bisexuals being friends in a big city is so implausible, really.