I have just learned that Google has recently updated the publisher policy page for Google Play Books. Gone are the mentions of book bundle pricing, and in their place Google has added several mentions of ebook rentals.
The mentions of rentals are vague, and there's no hint of how long one might rent an ebook for:
The "List Price" allows non-agency publishers to recommend a price for a book on Google Play. The Specified Price is only a recommended price and may not be the final sale price of the book on Google Play. For books that you authorize to be sold for rental periods, currently Google allows you to provide a "Rental List Price" for each authorized rental period as a percentage of the ebook list price for the book.
Amazon, Barnes & Noble, and many other companies offer digital textbook rentals in addition to ebook sales, so it would make sense for Google to jump in to the market. In fact, I would bet that Google's rental plans (if implemented) will look a lot like the manner in which Amazon rents Kindle ebooks. Amazon offers a variable rental period with a sliding price; the quoted text above is sufficiently vague that Google could be planning to do the same.
But just because we see the new policies does not guarantee that it will happen.
On a related note, the Google Cache of the old page (dated 23 June) reminds us that at one point Google was considering offering a print/ebook bundle for a single price. That never happened, so far as I know, and there's a chance that ebook rentals might see the same fate.
IMO the more important news today is the changes to the file formats that Google will accept from publishers and authors.
Google has dropped support for the wide variety of ebook formats they used to accept (Epub, Doc, XML, HTML, and even Mobi & PDB) and slimmed down their acceptable format list to only Epub, Epub3, and PDF (but only if no Epub is available).
This policy change represents a paradigm shift for Google. They're no longer looking back at the past in order to see how they have to catch up to the rest of the market; now they are looking forward to the future. Google is looking for a way to get ahead of the competition.
That is why Google is explicitly accepting Epub3 as well as Epub. Like Sony and Samsung (other also-rans of the ebook market), Google is working to stay current with the larger Epub market (and play catchup with Apple, which has been supporting Epub3 since May 2012).