We do have horizontal menu in our plans, though it is much more complicated than adding a theme.
We do have forum and blog pages - though of course not as advanced as dedicated services specializing in that.
Redirect from a menu item is being considered, though you can implement a decent workaround now by creating an intermediary page and adding redirect code to its header.
So new themes will only provide new visual designs, but same structure/functionality.
Dmitry Buterin, Chief Apricot