> a basic book, with key concepts, written by one person [...] without huge amounts of detail

For math and physics you can get pretty far with definitions and key formulas. As for succinctness of the explanations, it all depends of the "level of description" for the coverage. The more math notation used, the shorter the text will be, but also less readable.

In addition to the notation, you must control the vocabulary and the level of abstraction which you use in the narrative. The language level in advanced math textbooks is level="grad student", most science textbooks assume level="some college", most science news articles are level="high school", general media assume level=middle school", except Fox and CNN who give primary-school-level explanations of World politics.

In my experience, writing explanations for the "some college"-level readers can be quite succinct so I think your idea of a pared-down minimum viable textbook is possible. For example, a short intro to machine learning could start from 100pp of short-form lecture notes that explains the basic ideas and formulas, solved example problems and maybe some code---godda have some code in there if it's about ML. Writing such a text is just 6 months of work, whereas writing a full ML book would take years. Once the basic notation, definitions, and math prerequisites are written down, there could be 20-30 separate applications chapters (10-30pp each) where a single idea of ML is described by someone knowledgeable about it (perhaps not a researcher, the best would be a grad student). Bonus points for complete code examples. Pull requests for typo-fixes and requests for additional explanations ensue. And Bam!, ML textbook v1.0 done. A textbook in a year.

(v2.0 one year later can add more applications, add applications of the applications, or additional introductory material (tutorials) to make the book more accessible.)

> it is often so jarring when I read a journal article with different writing styles,

I think this will be and important problem with book-collab projects...
How do you meld the voices (and egos!) of 30 people in a single narrative?

> I understand that "getting your name out there" is not motivation enough for doing such things. However, surely just doing it for the good of education and teaching is motive enough?

I presume you must be under 30 from your statement since: Anyone who is under 30, and is not a leftist, has no heart; and anyone who is over 30, and is not a capitalist, has no brains. (http://en.wikiquote.org/wiki/Winston_Churchill#Misattributed)

There must be some sort of monetary incentive. Maybe "book writing" funding from fed-gov or prov/state-govs? Maybe paid by universities? Either way there must be money involved if we want to motivate people to invest one year of full time work to write a book on subject X. Making money of the printing seems like the best choice to me... and, interestingly, charging for printing is totally compatible with GFDL.

I think print-on-demand and self-publishing is a good first start---it puts more power in authors' and readers' hands, which are the only people that matter in the value chain. It's going to get very interesting in the book publishing sector in the coming years, I promise ;)