Scott suggests that higher level abstractions such as control toolkits will take the place of HTML in the future. I do not agree, mainly because I have seen how painful such approaches can be when you want to simply generate HTML. Remember, for an abstraction to be useful, it has to give me a significant advantage over the existing approach, and it shouldn't limit me overmuch.
HTML is dead simple, so I don't see much value with that, and since no control toolkit can give me what I want, and since when I need to add additional stuff, I want it to be simple, I don't really see much value in going in that direction.
What is possible is that technologies such as Flash / Silverlight would become much more pervasive and allow us to move from HTML documents to more elaborate methods of communicating with the user.