This is exciting, but... I wish they hadn't gone the route of hiding app controls behind a swipe menu. The menu button on Android was one of the reasons apps for so long seemed unintuitive on the platform, and the Windows 8 charms menu has been panned by critics for the same reason. If your users can't see the controls, they won't know they're there — and even though they could open the menu, it won't feel immediately intuitive in the way that just seeing the controls onscreen does. Even a little breadcrumb like the now-common triple-dash icon on iOS or the triple-dot icon on Android helps people find their way around unfamiliar apps.

Android finally dropped the hidden menu after the 2.x series, but it looks like Canonical just walked into making the same mistake.

That said this is very, very cool. Using non-mainstream programming languages on phones will be interesting.