As you may know, Canonical’s Ubuntu Touch is used by default on Meizu MX4, BQ Aquaris E4.5 and BQ Aquaris E5 and officially supported on the LG Nexus 4. While the BQ phones are mid-range, Meizu is among the most popular phone vendors in China, the MX4 being a premium headset.
Some users may not like Canonical’s strategy to use their mobile OS on a few devices only, but Mark Shuttleworth thinks that this is actually a good thing and not a bad one.
While Ubuntu Touch is already usable, it is not yet ready for mass usage and so, using it on a popular brand like Samsung would not do any good. For now, it lacks popular apps like WhatsApp and cannot compare to Android and iOS yet, but it has a very good growing potential.