I don't quite get what's going on here. Is this an idea for a major commercial product or is it a quirky fun thing for the ubuntu community? The scale they're aiming for seems to imply the former. Usable as a desktop is a cool idea, but more of a "linux on your wristwatch" idea than one with real use. I mean, if you have a keyboard & monitor handy, how hard is it to have a PC too? Cheap micro desktops are coming out…
It's a phone! It's a computer! It's both!
More seriously, imagine a phone that is always a phone unless you want to make it a computer. Plug it into a TV/Monitor/glass and you have a full computer desktop.
I travel quite a bit. I have in my bag at the moment a laptop, a phone and a tablet. With this, I need just the phone.
I also used to work in an office. When I went home, I had a computer at home. If I never wanted to do anything, read an email or what not, I needed to VPN in or sync something. Things ALWAYS got out of sync. Now, I can just plug into a monitor and have my work system at home.
Or, say, you are a corporation. You have 10,000+ people. Assuming you are a normal corporation of that size, many of those people have phones AND computers/laptops. It is highly likely that a very large number of those people could get by with one device: a phone that is also a computer. Cost savings for those corporations would be huge.