Before the start of this test would have made no sense to make a change like this, but its getting more and more evident that things just aren't going Hussey's way atm, he is trying his level best, but still he is struggling, so as harsh as it may be, dropping Hussey in favor of Watto would be fair enough, but before that Watto would have to prove his form and fitness in the practice game.
If the core-group still wants to back Hussey, then North would have to be the unlucky one to miss out, if Watto is fit, he has to play, his all-round skills would certainly lift the Australian side.