InfoQ had an interesting article recently asking Is XML the Future of UI Development?.
Historically, web developers have a knack for doing the impossible and making their imperfect platform bend to suit their needs.
Another point is made about Gran Paradiso, aka Firefox 3, with the assumption that relying on a single browser will make it fail as a platform. If anything, I think that this development will encourage further innovation among other browser vendors, as well as the creation of things like the Dojo Offline Toolkit to improve browsers until they add support for high-demand features.
Finally, the article fails to mention Apple as a platform at all, which is ironic given that all of the innovative desktop applications I have seen recently are OS X only. There’s a presentation scheduled for WWDC 2007, Designing and Developing Hybrid-Web/Cocoa Applications that looks to be very relevant to this topic:
The pragmatism of groups like the WHATWG shows that improving and fixing what we have rather than starting from scratch is much more likely to be adopted. Browsers, developer toolkits, and plugins all provide improvements at different points along a product lifecycle to add browser support for features such as offline mode. With the proliferation of multivariant devices, other desktop app features are needed for an application to effectively compete with desktop apps (e.g. camera access on an iPhone). By continuing to bend the platform we have today, Ajax and the open web will continue to prevail for the foreseeable future.