Yes, you can do this today.
Let's say you were going to make a book for a year's worth of articles. Here's what you'd do:
- At the beginning of the year, with the publication of the first article, you would make a new Leanpub book. State what you are planning to do for the
year with the book in the About the Book section.
- Either charge what you think is a fair price for the year of material, or start by selling it cheap, and raise the price as the year progresses, to reward early customers. Either way, everyone who buys the book gets all the material -- people who buy it earlier just get it sooner.
People are used to purchasing in-progress books on Leanpub, and everyone who buys a book on Leanpub gets free updates for the lifetime of the book.