I guess it depends on what Sasuke and Shikako, as the two full gems, know or don’t know about fusion. And whether or not they know Home World’s opinion of it (which I’m not even sure what that opinion is in this AU, anyway)
I feel like Sasuke and Shikako both know about fusion in theory but have never fused before–Shikako because, as far as she knew, she was the only gem left on the planet; Sasuke because he was the youngest obsidian (and obsidians generally didn’t need to fuse anyway). But I also feel like the first time any of them fuse it’s Sasuke and Naruto and on accident and more about the fact that Naruto is half gem half human.
Shikako is far more interested in the technicals of fusion involving a half gem half human and what that means for the two species. Kakashi is frankly weirded out that fusion is even a thing. Naruto is excited because he has been having trouble with his gem powers (wasn’t even sure he had gem powers).
And Sasuke meets the Kyuubi.
Internally, of course. Externally, Carnelian is more mystified at existing than anything else.