It might make more sense for window controls to also be status applets, since not all windows can be minimized, maximized, or closed. For instance, if a particular window is no longer needed and only showing some completed action, the close button could turn green. If there's an error, it could turn red. If a process could take a long time, a progress bar could appear and the minimize button could turn green. If a web browser could show a web page better with fullscreen, the maximize button could turn blue. This would follow the applet colour coding scheme.

One could even add some custom window commands (such as resize to content) to their applications.

Yeah, but I don't know why they couldn't have just said "We're moving the buttons to the left to acclimate users and make way for a new feature we'll be introducing sometime in the near future, but are not ready to discuss right now." It would have been a lot nicer than their "because I said so" deal, which actually cost them at least one good developer (to my recollection; there was a story about it on here not that long ago, but it would be hard to find) who felt that Canonical became calloused to community desires.