Aero
I think you may becoming overly concerned about the testing of this skill-set in the Sim. It begs the question, why not? As you already say
95 percent of routine situations can be coped with standard phraseology
well unless that is a figure you plucked out of the air (excuse the pun) there is another 5% of situations to be resolved.
During the LOFT scenario, in my humble opinion, no mental capacity should be spent for plain language! If not, I fear that one day there will be a major incident/accident where the human factors studies determine focusing on "plain language" during routine cockpit work as one important factor that has led to miscommunication and to the resulting catastrophe. This is what I derive from my studies so far.
Mental Capacity is lost by carrying out an unfamiliar task or a difficult task that has not been practiced regularly. Why not practice plain language in the sim? When you say 'this is what I derive from my studies so far', what studies do you mean? What were your studies that have led you to these conclusions.