There are 2 likely routes for the development of user interface software on the web.
The idea is to migrate applications back to a central server. This is analogous to the X-windows system that has been used on UNIX for a decade now. While HTML tends to put more intelligence into the screen (browser, or X-server), the architecture is similar. Such applications will presumably suffer from the same performance problems that X-windows applications do.
Network improvements could make a dramatic impact here, either transport improvements or network execution of server code.
Computation occurs at the workstation, so response is rapid. It's not obvious how an information provider gets paid though, or protects their intellectual property.
Does a HotJava applet have the ability to access the network and request data from some server? Security? Who pays for the accesses that an applet makes?