Always cool to see these in action, but multiple "online desktops" have come and gone since the mid-2000s. I personally built one myself in 2010 only to realize it had been tried and failed a few times. My next instinct was that to get attention and attract users I'd need a mobile-style UI. My instincts were wrong, and your gut is right. There wasn't a strong enough use case.
The motivator for these projects is typically something along the lines of, "it would be great if there was just one OS or interface I could use on any device." As engineers it's very easy for us to see the usage pattern of apps, the speed, power and ubiquity of web tooling + JavaScript and say, "aha! The next logical evolution is all of your client logic on the web!"
Alas, if it were only that easy.
"Unfortunately, this ability to see patterns can prove catastrophic as you attempt to build your own company. The more you generalize the solution to a particular pain, the further removed it becomes from that specific pain. While it might end up being able to solve a lot of pains, it won’t be very good at solving any particular one." [1]
A shared, web-based environment is probably where everything is going. I mean we're more than halfway there with most operating systems, cloud backups, tons of SPAs, etc. The problem is there's no consumer-driven need for a fast transition to a JavaScript "OS" environment. Everything is just good enough, and offloading all device logic to the web, for the end user, is barely noticeable (if not a minor detriment as older devices still have rendering issues). It's likely that everything will converge on this sort of environment (but without the desktop metaphor) because engineers want to head towards elegant solutions, but it will take time. (You won't convince people to start switching with software alone if it means they have to figure out how to open Chrome / Safari / Whatever on their phones, first.)
FirefoxOS [2] is probably getting pretty close. The sooner we get to an OS just being a glorified web browser, the more we drive development spending way down and cut costs for the consumer. Then the software will already exist, packaged with the phone. But you need the phone first --- not the software. That's the product. That drives consumer demand. "JavaScript OS" becomes a reality as soon as web-rendering matches native performance on ubiquitous, low-end devices. The software will exist to sell the product, not vice-versa. (We'll also have a Cambrian explosion of offline-first front-end tooling. ;))
... Yeah, I've done a lot of thinking about this. ;) Was my first big pet project.
[1] http://degoes.net/articles/engineer-entrepreneur/
[2] https://developer.mozilla.org/en-US/docs/Mozilla/Firefox_OS
