Chinese tech company Hisense is preparing to release a midrange smartphone integrating a second e-ink display on the back. The concept is not new, the Russian Yotaphone 2 did not succeed due to high costs.
http://www.notebookcheck.net/Hisense-to-release-the-A2-Android-phone-with-second-e-ink-display-soon.186794.0.html