I suspect we will get Astute class as UK shipbuilding of Astute class will be running down in not too distant future. Aust will build them in Australia but with a lot of stuff made in UK. Apparently US needed to give approve for UK to sell some of their nuclear reactor tech to Aust..
I also can’t see us getting 12 subs now. Fewer needed given nuclear range and speed. This will mean easier for us to crew them (even though they have larger crews) as submariners are not in plentiful supply. However we will need to get a lot of new crew and maintenance skills that will take a long time to mature. A lot of help will be needed from US and UK for basically ever.