Node.js + WebKit (or Gecko?:) HTML5 UI desktop Linux
The WebOS concept has been tried a number of times, and failed every time. Most spectacularly with HP blowing about $3 billion in the process. There's really nothing stopping HP's WebOS to used as a desktop OS, and it'll be open sourced later this year.
webOS didn't fail because of the technology choices, but simply because of mismanagement.
Have you tried the TouchPad? It was miles ahead of the Android user experience of the time (and in some cases also ahead of iOS). Shame that the hardware sucked.
I hope that Mozilla will be able to reuse some of the ideas (and code) from there now that webOS is becoming Open Source.
It failed for a couple other important reasons too. A web desktop is an anti-pattern. With my current OS I can already open a web browser fullscreen and access web apps on the internet. And I can also do other things like attach peripherals, copy my music and pictures, use photoshop and desktop publishing. I don't gain anything by abandoning my current OS and restrict myself to web apps. There never was any killer apps for WebOS, or any real reason to switch.
