I think this is the best way to give a incredibly jarring and downright ugly presentation. People keep talking about doing this but I never hear a dev suggesting it, there must be some reason that others are not seeing that makes it either not worthwhile or hard to implement.
The whole point of the display planes is to render the compositing unnoticable.
Take Alan Wake for example. That game is composited from several different resolution sources and it is one of the best looking games of last gen. In fact, I would hazard a guess that Alan Wake was significant driver in the adding the 3rd display plane.