So it looks like of the big 3, KIX will be the least prepared and no thought at all has been given to Haneda, which has a number of international flights, although apparently that doesn't matter since no U.S. carriers are involved!
Adding 100 extra officers to Narita has the following effect: in each direction, I think (not sure) there are 2 places to go through in terminal 1 and 2 places in terminal 2. So that is 8 places where a passenger can interact with immigration. It takes 4 shifts, 5 if you have holiday time and vacation time, to cover 24/7, so doing the math, that means at most 3 extra positions open, on average, at each location if they have forced overtime for immigration staff.
With the additional time required, apparently on both entry and exit, this small an addition is, of course, a recipe for disaster, espcially with tired officers forced to do overtime.
Also, where are they going to get these extra immigration inspectors? Will they pull them off visa processing? What happens when they decide they no longer need the extra staff?
Whatever the mess is like, I will be experiencing it in 2 weeks. My condolences to those who have to experience it before I do.