Edit. I actually only read the first page of the thread before replying because the forum lagged a lot. I see that many people addressed the "m!x problem", so I guess I repeated a lot here
My first thought was "I just don't care, and I've never even thought about this before (even though it bothers me in many other franchises!)", but then I remembered two things.
First, it was honestly kind of inconvenient and annoying when I played my m!x. I'd get 10 girls in a row even though I was just trying to get the genetics of one of the female tamagotchi into my family tree.
These new generations were games where you got a lot of your fun out of breeding your tamagotchi to look a certain way, and this ended up being kind of frustrating because it just randomly limited your choice in partners.
It didn't help that the female characters all shared a similar aesthetic, as did the male characters; what I'm saying is, if you wanted a sparkly glittery aesthetic in your family tree, you had to marry one of the female tamas.
In a game like this, I think magic items to increase your chance of getting a boy next (or something) would be quite nice. Obviously, removing the "hetero restriction" would have also solved this problem.
I feel like the gender was actually already a pretty unnecessary stat in the m!x... since your character always ended up with very androgynous designs. You could breed female Mametchis as well. I don't think it affected anything else either, like behaviour? Just restricting who you can marry.
I also do think that the "caring for your tamagotchi" mechanics have been a little lacking, so perhaps I focused on the breeding aspect a lot more than might have been intended. But that is another topic.
The second thing is that Tamagotchi are very humanoid; I've still been treating them like pets a lot, but really, they are just full-fledged people now. Have been for a long time.
Would be funny if your characters could randomly turn out bi or gay, and refuse to marry the partners you suggest if they are not the right gender. lol. Not saying this is a good idea, giving your tamagotchi such fleshed out personalities and lives that they can even have sexualities.. I feel it would just be a different game at this point.
I think this is also why I didn't feel there was a need for this; tamagotchi aren't even fleshed out enough to have a straight personality (sounds so weird) right now.
Well, the best way to implement this now is probably to just remove the gender stat. Like I said, I think it is not even affecting anything anymore, really?...
If they remove stats, just how they removed weight, it would be cool to introduce a new stat "to make up for it"; so your tama is still as "unique, fleshed out" as before, if that makes any sense.