RouteProcessorSubscriber is quickly getting crufty. Especially after overlay and SCOTCH get moved over to the new model, it's going to be really gross.
So instead, let's move all of that logic to route enhancers, which is what RouteProcessorSubscriber really is. It just predates us having route enhancers. :-)
This patch (as soon as I have a nid) should change no functionality, but removes a hard coded list in favor of an easily-extensible mechanism that's easier to read. I think that's a win.