Yeah, at the end of the day it's an ambiguously worded tweet. It could apply solely to X-Men Evolution, it could mean if he started again now she'd be gay (or if he was writing her story for the first time in 2018?), which would presumably be both comics and other media?
Also, I use "gay" all the time because sometimes bisexual is too long, which adds more confusion.
It doesn't mean anything, but it's fun to speculate, especially for those of us who are hungry for more representation. Laura means a lot to many people after all, which is why she's found success as a character, so at the end of the day it's cool that people are invested in this tweet but it doesn't change anything until it's canon somewhere. I would definitely love to hear more from him about it though, so here's hoping we get that Jay & Miles interview.
Big bowl of speculation: I guess he *could* have building to a reveal that she's gay, maybe even with Hellion supporting her decision after some initial shock (who knows!), but the fact that Choi didn't know anything about is pretty strong evidence against that, plus the fact that I'd imagine Liu would have run with it (far beyond vampiric sapphic inference) if there'd been any passing of the torch between her and Kyle.
Maybe Editorial put the kibosh on it and he never said anything until now, never having reason to (c.f. Rowling and Dumbledore as mentioned above) and not wanting to rock the boat before he found success outside of Marvel comics?