It makes sense. Amazon.com has leveraged its Amazon Prime memberships for other things before, and the service is quite popular already, although Amazon.com has not revealed how many Prime members it has.
The Amazon Prime service gives members free two-day shipping on most items, and $3.99 one-day shipping (per item) as well. Earlier, in February, Amazon Prime members were given access to video streaming via Amazon.com's Instant Videos service.
Reportedly, Amazon.com would offer publishers a substantial fee if they participate in the service. Some sources said that Amazon.com would limit the amount of books that Amazon Prime customers could read freely every month. It's unclear if these customers could then pay "overage" fees to read more.
The titles would also be older ones, the sources added, and not current, timely bestsellers.
The Wall Street Journal implied the new service is not a done deal, by any means. According to their talks with several publishing executives, publishers are aren't exactly enthused with the idea, feeling it could lower the perceived value of books and also because it could put a strain on their relationships with other booksellers. It is unclear if any publishers have already agreed to a deal.