That's an interesting idea and quite the coincidence. Literally about 24 hours ago I was thinking about this same thing. Specifically, I was considering what it would take for me to write "JRiver Media Center, The Missing Manual".
Even borrowing lots of material from the Wiki it would be quite a lot of effort. It's probably even more than my mental estimates.
Honestly, one of the big motivating factors here is monetary. I would be much more inclined towards doing this project if there was sufficient compensation involved. In other words, being paid for my efforts.
I'm just not sure how many people would be willing to pay, even a small amount, for something like this. If enough people were interested and truly willing to pay a small amount of money, then it would be worth doing.
I'm not sure of the interest level. It might be higher than I think. Or it might be very, very small. It's hard to estimate this kind of thing.
The scope of writing a JRiver MC "book" would also be a consideration. I would necessarily want to omit certain features that are either extremely complex, or that I have no experience with, or both. The biggest one of these would be the TV feature. It's very complex, changing very rapidly, *and* I have no experience with it.
Anyway, interesting that we were both thinking of this at almost the exact same time.
Brian.