Plus Q can assign from the 737 to the 321 if they deem there is a surplus of 737 pilots.
Sydney is the first base, apparently all of Sydney will be changed to the 321 before any other base gets a look in. Of course their plans never work and this will be over a significant period of time. Expect it will be quite a junior fleet to begin with due training freeze, until they get to the point where there are no more ‘unfrozen’ 737 pilots who want to go, then they will look at frozen pilots who want to go.