It's a great book. It is really impressive just how forward thinking it is. I guess I shouldn't be surprised, Feinberg is the GOAT. I find a lot of the discussions in the book have an even more progressive outlook than many current conversations. I'll hear queer people people splitting hairs about labels and arguing how gender works while Feinberg just lays down facts and is pretty much always correct.

S/he wrote a pamphlet on it, don't remember the name though. Although I've heard there's some slight problems with its history but I wouldn't know. I thought it was a good read.

This is an awesome book. I've used it as a 101 resource for a couple people and it's perfect for that. Like you said, it's very accessible, it's so human and compassionate, it's easy to read in snippets, phenomenal.

So the pinned post doing a gender survey made me think deeply about this. This is how I answered:

I guess I say no here. I present masc, and definitely lean that way, but I've come to realize that a lot more people are gender fluid than think they are, myself included. It's all kind of silly how we get drilled into our heads what we are supposed to be and how we're supposed to act, when we are all our own unique individuals.

Like I am totally fine using he/him the rest of my life and and have no strong desire to identify as anything else. I did a little reading and I guess "demiguy" comes closest? My issue is I don't think AMAB taking an introspective view and seeing that not all of society's masculine norms apply to him should need a definition. Defining it like that just feels like an extension of the binary idea of gender. It's a weird feeling.

I guess I'm asking if that book you read has any answers or perspectives on my thoughts, or if the way I feel about even needs answers?

Could anyone recommend a book that goes over non-cis gender identities throughout history and the roles they played?

No, but I'd strongly encourage you to send an email to Michaela Appletova because she's an academic who is interested in history and gender identities.
Your question isn't squarely in her wheelhouse but academics know academics and they move in the same circles where they share overlapping areas of interest so she would probably have some good names of authors or books to point you towards.

Academics, especially historians, are generally massive nerds and when someone is polite and shares their interest they tend to be extremely enthusiastic about the whole thing particularly when it's someone from the general public. (It can feel a little bit claustrophobic and insular being stuck in a university office toiling away for years or decades at your subjects of interest and wondering whether you're just shouting/typing into a void or—worse yet—to some little self-congratulatory academic circlejerk.)

Here's her info including her email:

https://history.wfu.edu/people/appeltm

I guess I'd encourage you to keep the email pretty brief and don't feel discouraged if it takes a few weeks or longer to get a reply. Often academics are overloaded with stuff like deadlines for marking work or submitting things for conferences and stuff. Or they'll be reaching out to their contacts to get the best info to you.