rooting isn't hard. putting Ubuntu OS on a phone designed for a completely different system is a bit more risky than flashing a custom ROM meant for your particular device. and as i recall, Ubuntu OS's support is still extremely limited on devices. besides, Unity is the same simplicity crap as Play and Windows 8. sad how everything is now taking cues from Microsoft in the element of design, including Linux. perhaps a Kubuntu release can be possible eventually?
Who the hell wants to use a dongle or hard drive attached to their phone over a microSD card? some of us use their phones as music players while out. assuming the cloud is so great, what happens when you go into a no-coverage area? the music STOPS. that is when offline copies stored on an SD Card come in handy, and benefits include not hogging the internal storage used for apps and games.
Dongles and external devices connected by a cable. say hello to PC Cards and RS-232 life again. it may look and work differently and faster but still...same thing.
Samsung Galaxy Precedent (rooted, AreaRom 3.4 , sd-ext w/ 3.65GB internal space)
Kindle Fire (1st Gen, rooted, AOKP JB 4.1, Nova Launcher)
Samsung Galaxy SIII 4G LTE (rooted, Carbon ROM)