Ubuntu needs a way to install onto non-rooted Android phones, simply by installing an app from Google Play.

There was a lot of fuss about Ubuntu on Android, and there's lot of text here: http://www.ubuntu.com/devices/android it mostly advertises Ubuntu to cellphone manufacturers, but it misses one point - those guys are driven by money and business, and they are not interested in anything that does not show immediate profits (even if that's something as simple as rooting your device and unpacking tarfile). So, Ubuntu needs an app, a simple app that non-techies can install on a phone with a single click, and it needs to get some resonance among users (1 million downloads would do). Only then manufacturers will recognize Ubuntu as a market trend and a business opportunity, and will possibly make dual-boot phones, because Ubuntu support will bring immediate profit in their eyes.

There are already several Ubuntu installers for rooted phones, they are not insanely popular though, I guess because of the root requirement.