Google has updated its support pages to reflect expanded availability of Play Books. You can now buy books from Google's store in Bulgaria, Croatia, Iceland, Slovenia, and Slovakia. If you're a physical book person, move along and pretend the future doesn't exist.

2015-03-19 17_18_30-Country availability for apps & digital content - Google Play Help

If you live in one of these nations, you'll be able to read Google Play books in the official app. Any DRM-free ebooks you have can also be uploaded to Play Books and read in the app. Google allows authors to publish without DRM so you can even export copies as standard epub files to be read anywhere. This is a feature I took advantage of when I published a novel last year, and it's something Amazon doesn't do.

Google reverts page

Google has removed mention of the new countries from the support page, and Books does not appear to be live yet. Someone probably pulled the trigger early. I imagine these regions will get Play Books soon, though.

Google Play Books & Audiobooks
Google Play Books & Audiobooks