Shell could have the ability to "zoom out" to a view of all the currently loaded web pages presented as tiles which can be "zommed in" to. Something along the lines of Expose in OS X or Panorama in Firefox.
Tabs could be grouped into workspaces and those workspaces could presented as a row of tiles.
Alternatively the workspaces themselves could be the tiles
Group "pages" into "apps" and apps into "workspaces"
Could home screens and workspaces exist alongside each other?
Making the web browser behave like a window manager for web apps
- Each tab limited to URLs withn the scope of the domains defined in the app manifest
- Clicking on a link with a URL outisde this scope creates a new tab (a generic "browser" app?)
- Tabs are grouped into apps'