Yeah, I have mixed feelings about some of this.

Disclaimer: I don't care that much that they're not staying close to the books material-wise. I already have the books, and I'm much happier with a spiritual adaptation than with a super-direct one. With that in mind, Cheri being non-binary rather than a woman is fine, as long as the character beats are the same. Carcer sounds like they're combining a number of Watch villains into one major antagonist, so I can get over him being very different from his book presentation, and his blackness is less of a big deal with Sybil also being black, because it's not an "only black main character is the wronged criminal" situation. Similarly, flipping Carrot and Angua's training is fine, and could even present some interesting character moments as he grows into the role and takes over.

On the other hand, I'm waiting to see more about Sybil, because count me in the camp that really liked her as a practical, heavyset woman who knew how to wield her noble status like a cudgel to make the world a better place. Sybil is such a great character that altering her instantly makes me nervous.

A lack of casting announcements for Fred and Nobby might just mean they aren't going to be considered leads, which honestly they aren't in most of the Discworld books. No Detritus is a bit more sad.