I’m not here to stop anyone from having their headcanons. If that’s what you think, then you are free to think that. Have all the non-binary Riley headcanons in the world. Even though I don’t really share them, I have nothing against non-binary Riley headcanons (unless you try to use her hockey playing as a reason for thinking she’s non-binary.)
But don’t forget that making Riley non-binary was NOT what Pixar had in mind when they created her character. (Let’s not turn this into another “OMG Oaken’s gay and that guy who looks like a 15 year old version of Oaken is totally his lover and not his son” fiasco and put a studio on a pedestal when they actually didn’t intend to do anything revolutionary.)
The other characters’ emotions were made to look like the character whose head they were in so that when people saw those emotions they immediately recognized whose head we were looking into. If the emotions looked the same in everyone’s heads, it’d be harder for the audience to say “okay now we’re in the mom’s head. Now we’re in the dad’s head” for the 5 seconds we’re there before it flashes away. A quick read is also the reason everyone had the same emotions running headquarters, even though in reality, everyone’s headquarters would probably be a little bit different from everyone else’s.
As to why Riley’s emotions are different genders, I remember reading a post on here that said the genders for Riley’s emotions were chosen based on which genders felt more male/female to the filmmakers. I’d also posit a guess that they made them different not look like Riley so that they’d be cuter characters with more recognizable looks. The toys would be a lot less cute if they all had Riley’s haircut. (Not that her hair isn’t cute. It’d just be a bit strange if the toys looked as they did now but had dirty blonde doll hair). And, sad as it is, if ALL of Riley’s emotions were female, there are plenty of little boys who wouldn’t want to go see the film. (Which isn’t really their fault. Unfortunately, parents still tend to teach that stuff to kids, and in my experience working with young children, they tend to really care about gender stereotypes, especially the boys.)