Boeing changed their terminology to come into line with some US CRM thinking (blowing in the wind?); alternatively, Airbus has not, although they did discuss the subject.
Labeling people or their jobs can polarize thinking and constrain some activities. Monitoring is a valuable safety tool, but it is also a complex subject. In reality both pilots should be monitoring, first the aircraft and the environment, second themselves, and then other people.
Alex you perpetuate a common misunderstanding that it is possible for one person to monitor another. Whilst this may be true for some physical actions, it may not be so for the many thinking processes – situation awareness, decisions, plans, thoughts, the failures of which often lead to accidents.
Thus, the act of monitoring should be on the output of thinking to include both the thought and action. The best way to achieve this is to see what the effects are on the aircraft, what is happening, where it is going, then try to understand why. If the monitoring pilot does not understand what is happening (e.g. PF not following SOPs) or the result does not fit the situation then s/he must intervene – call out or question the pilot flying. Therefore, the task of the monitor is somewhat similar to a continuous threat and error management process where the ‘labeled’ duties (PF) will take action and the (PM) will intervene.
The best option may be to retain the use PF and PNF, these define the primary functions – where at least one person should be flying at all times; whereas there are many situations where monitoring cannot occur because of crew tasks and workload.