Will being gay, or not being gay isn't a major or minor plot point, it's a character trait. Same for the other boys all being straight. How relevant that trait is depends entirely on the narrative.
Now, such a character trait can certainly inform a plot point, like say Mike and Eleven's make-out fixation being a sore spot for Hopper, or Dustin (last seen repeatedly striking out on the dance floor) finding a girlfriend at science camp. But then these are hardly the only things that matter about these characters.
If for the sake of argument Will is gay then what difference would it really make? I mean besides adding an extra layer of depth to his feelings of isolation and "otherness", even among childhood friends, re-contextualising what we've seen of his family dynamic and give him something other than being "the victim" to set him apart from the other kids. Oh and representation for all the gay kids out there who could benefit from knowing they're not the only ones...yeah, it wouldn't make any difference at all.
Personally I get the feeling "queer" is sometimes like the n-word of non heterosexuals. As in it's a slur that's been reclaimed and can be used freely amongst them, but if you're *not* a part of that world then you should probably think twice before using it.
The only reason I think it'd be easier to use it more generally is mostly out of my own laziness. I mean "LGBTQ+" doesn't exactly roll off the tongue so well and all it's basically doing is trying to encompass everyone that isn't cis gendered herterosexual, which "queer" kinda already does. But then we run into the "it used to be much more of a slur" issue and we're back to hard to pronounce initialisms