I should say George Church (who’s absolutely smarter than me) thinks it’s plausible and good. We don’t even get much into detail, but a lot of molecules in your body exhibit chirality - like a corkscrew, one turns one way, another turns another way. A lot of molecules in your body have this chirality. So in principle, you could create organisms that operate on other chirality. So there’s actually an idea, maybe back in the 1980s, there was the idea of a sweeter that your body couldn’t use because it operated on the opposite chirality.
A more potentially interesting idea is presumably a lot of diseases wouldn’t be able to affect you if you were the “mirror” version. But for the amount of work it would take to make a mirror human, we might be able to cure these diseases! And Dr. Church pointed out if you have a mirror human and a non-mirror human, presumably they wouldn’t be able to reproduce. So you’d get this weird thing where you’ve created a divergent species that looks like you. And if they’re better than us with not getting diseases, they might not like us! So maybe we exist in a world where the mirror people take over.
But plausibly, suppose you wanted to do research with smallpox - you don’t want to make any mistakes as no one’s immune to it anymore. But if you were able to make mirror smallpox in a lab, you could do these tests and it would immediately die out in the wild. But mostly it was something we read about that George Church (who embodies mad scientist in every wonderful sense of the word) wrote about extensively in his book REGENESIS.