Regarding Con 5), it's generally true with some exceptions. I wrote a Fortran book (https://www.manning.com/books/modern-fortran) and expect it to stay fresh for at least several years thanks to the slow pace and the unusually high maturity of the technology. On the downside, it's a relatively narrow niche so I don't expect high total number of sales. For instance, about 800 copies have been pre-ordered in the first 2.5 years of writing. The book is done and will be out in print in November.