Any single book can be selected as a Super Selection and after it is a Super Selection for 3 months, it is converted into a hardcopy. (drop shipped to your address)

Books accrue Super Selection points continuously, and there is no penalty for switching a Super Selection at 89 days to a different book.

So for the cost of printing and shipping at most four books a year, O'Reilly entices the reader to maintain a longterm subscription, with the benefit of knowing they'll recieve a hardcopy as a bonus every 90 days...Perhaps this option would best be offered at the $20 a month and above level. Of course someone familiar with the economics would be able to select the best pricing point. I know as a consumer, that I would consider a valuable incentive.

This would actually be nice for, subsequent editions, where you want a refresh on a hardcopy you already bought...

The marketing department would be able to see what books are considered long term value. Perhaps the classics in their fields.