Well the banks have been subsidising borrowers from increased borrowing costs. I don't think they will increase NIM at all. It will decrease further. Executives like Commyn, as head of the retail bank, have been negligent in their job pushing quantity over quality. (I sold my CBA shares when he was appointed. He is useless).
Increased borrowing costs would increase the hurdle rate for business so they would be less inclined to borrow. I could be wrong, of course, but these are the assumptions I have currently made economically.