PJ2, it would be difficult to do better than your exhaustive answer. But to help (maybe) answering the question "switching deliberately from alternate to direct law" and as a former airbus driver I knew that at least, what would come to mind when you are not a test pilot, when there is no test flight engineer sitting back in the cabin with all test equipment would be ...lower the landing gear. You are in direct law and you put your hand on the trim wheel and you understand, now, what your trim balance is ...sorry if this seems very simple-minded and even stupid, but when you are lost with out-of-trim airplane and inefficient stick inputs, at least you go back to basics. It would have to be a very frightening situation to go to such extremes (apart from landing gear speed and altitude limitations which you maybe would not care about anymore) but it might save the day, only, of course, considering that the alternate law might be going mad at the absent airspeed(s) informations.