Fifteen years ago it was the web browser that was going to blow the desktop OS to smithereens. Larry Ellison announced the "network computer" that had no local storage (i.e., no hard drive) booted from the net and revolved around the browser. Although the web browser has become more important over the last 15 years, the only thing we have today that resembles a network computer is the Google Chromebook, and the only people who have those things are people who got them below cost and want to replace the (Chrome) OS with a desktop OS and (returning to the theme of the OP) people who really really really love the web.

There has been over 30 years of research and field experience with the WIMP paradigm. The code bases (source trees) for the three most "popular" (most relied-on) desktop OSes are over 20 years old. (Yes, I know that the code base for Windows XP and later differs from that of Windows 98 and earlier, but the code base for XP and later, namely, the NT code base, is itself over 20 years old if you count the final 18 months or so of its pre-release development.) I concede that there is a good chance that iOS and Android and Windows Metro will eventually kill the desktop OS, but that is going to take another 10 years and probably significantly longer.