Harold - as you know, I am a huge fan, so I encourage you to go further. I was just reading Seth Godin's blog post for today wherein he synthesizes 30 years of projects with some simple explanations.
http://sethgodin.typepad.com/seths_blog/2014/07/thirty-years-of-projects.html
Read it and consider: "What's the most I can do?"

What would be a good book title/sub-title?
"mastery" is a word du jour, especially since Pink has been banging on about it, so there is an element of power to it that I like.
sub-titles tend to be self-helpy so buyers can put themselves in the front seat - "this book is about me!"
eg How to become a better colleague, lead from behind, kickstart fantastic projects and get ready for the future of work...

Does the term “personal knowledge mastery” make sense to a general audience?
Think of Godin and the great marketeers, there is a certain sizzle to their work that opens the content to a greater audience. "PKM" sounds very earnest. Think about what Brian Solis did with his WTF book with gapingvoid cartoons. He essentially took some quite deep, dense, dry content and sexed it up. My guess is that is not your style, but when you are dealing with dark times and shifting sands, some lightness of touch goes a long way (unless you are a polemicist).

Is a book on PKM needed now, and if so why?
yes, because of all the macro elements you write about in the way work is getting done. Your work is about self-ownership.

Am I the most suitable person to write this book?
Undoubtedly, and how to include / squeeze your network is an interesting idea...

If I wrote this book, would you buy it?
yes

Should I write a book on a different subject, other than PKM? (for example, my ebook covers several topics)
Well, you probably have several books in you.
Where is your energy and motivation? What topic most juices you every day?