You answered you own question. Gear books often are outdated. Any manual will become outdated, including yours. Gear is dependent on where you backpack, what kind of backpacking you do (weekend vs thru-hikes, for example), personal style. Most guidebooks have a section on recommended gear for the specific area. There really is already lots of information out there, particularly on the internet. There is no one "right answer". Backpacking is really just a combination of "hiking" and "camping".

I am not trying to be personal here- this applies to ANYONE who is thinking about writing a "how-to"manual. It is hard to sell unless you have already established yourself as an authority on the subject. What experience do you have to tell beginners "what the right equipment is for THEIR needs"? You are talking a huge variety of "needs".

However if this is an interest of yours, a labor of love, why not try? If you have the time and desire it would be a fun project whatever the outcome. Just the process of writing a book/manual will teach you a lot of valuable skills.