I can't edit, but I forgot to add:

No support for forms. The browser is meant for content consumption. Not for interaction/creation.

One could argue that any JS capabilities to do network requests (including dynamically rendering content) would be disallowed.

Yes, I know, this is going pre-Web 2.0.

Yes, of course, most current sites won't work in that model. But I'll also say: Most current content sites don't need these capabilities. They have them because they know the browser supports them.

Again - a fantasy. I know only a few people will use it. I know that won't be enough to change web behavior. It would be nice, though, if sites carried a badge to indicate they conform to all of the above.