Good point about the ma ai not being fixed Bryan but I am still not sure that one could say that you are still in ma ai during the execution of let's say irimi.
Ma ai as I understand it in both the kendo and aikido context is the point where you have to take a step to use your weapon (sword and handsword (tegatana), respectively) and of course your opponent must do the same. In ma ai we have the opprotunity to practice aiki - that sensitivity to your opponents every move since as you point out the situation remains fluid. A slight shift in posture changes ma ai.
Tonight its Judo night - I really wonder how one defines correct ma ai in this context.