I can see this work in the Java world through the community process and open-source organisations like Apache supporting it. Unfortunately, I still have to see whether similar traction can be formed in the Microsoft world, because Microsoft currently has no direct benefit from promoting richer browser applications. It would go at the cost of the momentum they are trying to build for development of smart clients based on XAML/Avalon and Office. Developing a browser-side framework would be a risk for Microsoft partners (or any other commercial party), because it is practically impossible to protect browser-side script. So I guess it will have to come from either the open-source community or a MS partner who is willing to build both framework and VS.NET integrated toolset.
A business model based on providing the toolset seems to be feasible: in the Netherlands BackBase is a company with a very interesting offering in this area (based on a open-source, Java-based backend).