I agree that so far the art and writing is very alpha, but there is a lot of potential in it and I hope that we will be able to choose our book's topic, style, length, etc, but still I had fun writing poems and reciting them in various fortresses.
You can sort of choose your topic. Once your character has read biographies, you can write them. The bio will be based on some NPC your character has interacted with. Or if your character's read about screw pumps, he/she can write about tech as a subject and the book will concern screw pumps. If your character has also read about cameras, then when writing about tech, your character has a chance to write about both screw pumps or cameras. This works.
Style of writing is based on character traits. If your character has a sense of humor, the writing will have humor presuming the subject matter allows for that trait to express itself in that written form. A trait like order can help with chronicles as they involve compiling info. Confidence as a trait results in florid writing, etc, etc...
The starting framework for creation here is great, but I'm hoping it gets fleshed out. Fighting has a fair amount of interactivity and success against certain creatures can draw on various things you know about gameplay, about the mechanics of this or that, require certain setups so that there has to be both character building and one's own improvement as a player. I'd really like to see non-combat receive just a bit of this.
One of my first, clearest and fondest memories of Dwarf Fortress was crossing a river for the first time in 34.11. It was a hot biome. There were fish. It was midday. As my character just stood on the riverbank, I took it all in. That can be a repeatable moment, but it doesn't serve as the connective tissue that interactivity provides. Interactivity makes it all replayable. YMMV.