Everyone working on Mozilla kept claiming it's a toolkit for building Internet applications, not just a browser? Yet, the first thing that was built was a browser suite. And then, once that came to version 1.0, they set about on a new project, and its goal was to build... a web browser.
I've been thinking about things discussed in this article lately, and I have shared some of the same ideas. I, too, think that the Watson style UI is better for finding the data people actually want. Web sites are very poor at this. They require search engines and extra tools to provide any kind of order.
Considering that Mozilla already supports RDF and XML and so on, there doesn't seem to be a Semantic Web Client in development. I'd start one myself, but I fear the way I would implement it would require destroying the entire Internet.