As reported by Julie Bosman in this week's New York Times, "Impatience Has Its Reward: Books Are Rolled Out Faster"
"While the television industry has begun catering to impatient audiences by releasing entire series at once, the book business is upending its traditional timetable by encouraging a kind of binge reading, releasing new works by a single author at an accelerated pace."
There's arguments on both sides - releasing the books quicker keeps an audience hooked. Leaving more time between novel releases lets you build that audience.
What's not mentioned is that the author still needs time to WRITE the books (unless the first book release is delayed until future books in the series have been written...)
For those of us writing/illustrating, or contemplating, series work, it's a fascinating development to consider.
Illustrate and Write On,