I think that waht Ubuntu Mobile has to offer is the ability to become a PC when connected to o monitor. Right now no other mobile OS can make this. In a certain way, is exactly the opposite of Windows 8 (and Gnome 3 or even Unity): one interface for all devices, wich means a mobile interface for desktops. In this case, we have an interface for phones and tablets, but when it becomes a PC we have the full desktop interface. Ok, it's Unity and I don't like it, but I still find ti better than Metro.
Other point that I find interesting is that the apps can be made in html. If Firefox Os gains any traction at all it could means that both can share the same web apps, with no need to write the same code twice for different systems.
Ubuntu has something new to offer, but I don't know if is enough to gain any market share, even more because 2014 is too far away.