I mean, think of the subject matter, on a children's network, that is being shown. This would be complete taboo even a few years ago. One can view this as progress, or a complete decline in our values system.
Eeeeh, Cthulhu always swims left. I think the idea that non-traditional romantic attraction represents a "decline in values" is drawing very close to the edge of today's Overton window.
Though I'm sure the mono/null-gender thing helped them get the show across the line a little earlier than it would have otherwise.
I particularly like that the show takes these things and just plays them completely matter-of-fact. Attention is not specifically brought to them, no one dwells on how anything differs from traditional post-classical norms, it's just how things are. Or at least that's how it was established in S1, looking through Steven's eyes, who'd never known anything else. Now that Homeworld gems are in the picture, they are making the distinctions more explicit. Which is fine, but I really liked it when these things were treated as unremarkable.