This seems like a lot of effort for something that will be unnecessary and unused in a month. I mean, it's cool, but they already have infrastructure for "demoing" remote apps, they could have demo remote instances with websocketed/vnc (noVNC, very cool).
For any other OS I'd agree with you. But for Linux desktop, which has come so far in the past 5-10 years, this is exactly what they need to show people "Hey, our desktop doesn't suck anymore! You should try us out again."
But it's not REALLY the OS's UI, is it....it's a bunch of HTML made to look like the OS's UI. Sure it might be indicative, but a video and some screen shots would also be indicative.
It's another medium. Interaction makes the experience different from passively watching a video. Plus there's the marketing factor in building this demo.
