I think I found a great solution for reading Windows 8.1 Book on Windows 8.1, which, when you think about it, is probably how many people will want to read it. Today's update of the NOOK app for Windows 8.1 adds a number of new features, among them the ability to sign in with your Microsoft account. And because this app can read on-device ePub files, you can use it to read a good-looking version of the book.
To use this app for Windows 8.1 Book, first download the ePub version of the latest Windows 8.1 Book document (version 0.12 at this writing).
Then, install and sign into the NOOK app. If you're not a Barnes & Noble customer, just sign in with your Microsoft account.
From the home screen, display the app bar by swiping from the top or bottom edge of the screen and then tap the Import button. Using the file browser that appears, navigate to the location on your disk where you saved the document. (If it defaults to SkyDrive, you can choose This PC from the top toggle.) Select the file and then tap Open. Windows 8.1 Book will appear in the home screen.
Tap the book to read it.
And don't forget you can customize the experience by using the edge UIs to display app bars with buttons for setting bookmarks and changing the text properties in many ways.
When a new update comes out and you wish to delete an old version of the book, navigate to the Home screen in the NOOK app. Then, tap the My Library: View All > link at the top to display the content in your NOOK library. Select the old version of the book and tap Delete in the app bar that appears.