Yeah. I feel it comes down to the Holy Blood mechanic introduced in FE4. So the whole genetics thing is kind of important bnreeding-wise, though in the next game, they could have some homosexual pairings and still have skills being passed down since they are "teaching it" to the adopted kids instead of it being inherited. They would probably limit the available pairings to only about 2-3 characters though, just to keep it slightly representative? I dunno. XD It wouldn't totally make sense having all the characters be bisexual or even half of them bisexual (let alone exclusively homosexual). But that would be awesome if they did! It just requires extra thinking to write.
Even the growing representtatuion of dark-skinned people is making slow progress, but it's coming along.. So - hope they continue with that.
Might as well not have gender specific classes at some point too. Male peggy knights and dancers, female pirates and berserkers, go!