TunesKit Studio has introduced iBook Copy for Mac (http://www.tuneskit.com/ibook-copy-mac.html), a tool to permanently remove the DRM lock from protected iBook ePub files. With the smart tool, the company says you can legally get rid of DRM protection from iBooks.
All of the original meta info is retained, including the book author, cover photo, publisher, data, and more. You can read the iBook ePubs on Kindle, Nook, Playbook, and other eBook reading devices.
Currently this smart iBook DRM Copy is only available for the Mac and is compatible with OS X 10.11 and higher iTunes 12.3. It costs US$24.95; a demo is available for download.