So, I'm pretty sure that it's rude to call someone out and say, "You, sir, are a remarkable idiot," but I'm about to do that. Consider it an object lesson, like "What Not to Wear"
This is "What not to wonder"
First thing I saw on my Goodreads just now. First off, bravo, Rothfuss, for doing some hardcore nonfiction reading that will enrich your writing. Now, on to the idiots.
N: You're a follower and a yes-man/lady. Stop abusing my smiley, there aren't many people who include the hyphen-nose these days and I would prefer that you didn't associate it with the idiocy of the other commentator. I don't know if I believe that you know what M.D. means because I'm not sure I do; his/her statement doesn't stand up to even a flimsy load of common sense.
M.D.: You have not read either of the first two Kingkiller books, obviously. Or you're stupid. I'm going with stupid because you're wondering about the third in the series and can't guess how such a book could relate to a pre-industrial society like the one in which Kvothe lives. Forges, water wheels, and cathedrals are all established elements of that world already; if you missed them, you aren't paying attention. Any other technology mentioned in the book would not only be technologically appropriate for the setting, it would more or less match about 90% of other fantasy books as well; middle-ages level is pretty typical. It makes a lot of sense for a fantasy writer to want to know more about that technology.
Meanwhile, you're "desperately trying to guess what aspect of the Gies book will work its way into the worldbuilding of book 3."
Let's examine that thought.
The world is built. There are parts we haven't seen a lot of yet, but Rothfuss isn't going to be doing any huge changes here. We might expect that he'll visit new countries, maybe even the Faen realm, but if any remarkable piece of technology becomes a turning point for the story I will be surprised. Desperate guesses about what sort of bits and bobs might fill in the scenery - what kinds of plows they use, for instance - is a waste of time.
Beyond that, why the heck do you assume that this has to relate directly to Rothfuss's next book? Is the man not allowed to read off-topic? If he's smart, which he obviously is, he's probably hoping and planning to write more books after the next one. Middle-ages tech is relevant to Kingkiller but not especially so. They have crossbows, but they also have machine refrigeration. That right there changes a lot; food preservation techniques aren't necessarily as developed, and wealthy people can have fresh meat more readily without the need to hunt it directly or even employ the men who do. There are even professions that specialize in moving cold-boxes from place to place, transporting temperature-sensitive goods. And this is just one minor wonder of the magic system, something Kvothe could fix as a minor favor and even create on the fly, with his fingernails and a piece of wood, in minutes. If you want to theorize about what kind of revolutionary technology might enter into it, assuming it would or could, think of creative things you can do with artificery or expect the invention of rifles or steam power. Or steam-powered rifles; sympathy could even create remote-controlled-steam-powered rifles. I'm kind of surprised that it hasn't already, actually. If the Bloodless can deflect arrowheads, similar sygaldry could be created to propel a small bit of metal at high speeds, especially with an energy source like a forge-fire or a boiler.... none of that could be in this book, though, you see? Rothfuss's world is way outside the domain of this text.
A book like this is meant to inform the reader about how things actually worked. I could write a story about a blacksmith and mention his forge, but since I don't know a damn thing about how a forge fire actually works differently from a campfire - except that it's pretty darn different - I'm certainly going to get a lot of things wrong. The story might work, but anyone with a scrap of sense will know that I don't know anything about blacksmithing or using a forge. That's the sort of mistake Rothfuss, being a reasonably intelligent person, would like to avoid, thus his choice in reading material. This was obvious to me the moment I read the title. "Oh," I said, "it's a scholarly text on technology of the middle ages. I'd like to read something like that sometime, if it's not too boring." (I didn't actually say that, of course; if I would have said anything, though, it would probably have been something like that)
You, on the other hand, said something like, "OHEMGEE, P_Roth is reading something, it must be a clue for the next book, oh I bet it's going to have medieval technology in it! I wonder what kind!"