Not sure buying a submarine with transit speeds 1/3rd slower than Collins solves any of our problems. Japan is very close geographically to China. Australia, is, very very very far away.
If we are talking about the new type zero proposed submarined based of Soryu, then it suffers the same problems as short fin Barracuda/Attack, it needs to be designed and built.
The Japanese are willing to help us, and we should use them and benchmark them, against the French continuously, to get what we need. But even the Japanese were completely sure about soryu based subs solving our problems.
Not all problems can be solved by walking in off the street and buying MOTS. Sufferen is in the water doing trials right now, so at the moment, the barracuda based design is the lowest risk out of the new designs. Collins II is basically going to happen, just with the existing hulls.
Kicking submarines is constant past time of Australia. They are a big, complex and expensive project. Possibly the biggest, most complex, most expensive project this country has ever done. Bigger than snowy, bigger than the harbor bridge, bigger than NBN, bigger than the AFL grand final.
They sit at the heart of the ADF high end capability. They are a magnet for critics. It drives clicks and sells papers.
The biggest issue at the moment appears to be local content. Which of course isn't an issue if you get a submarine wholly built overseas, but for many reasons, that is a more expensive and less favorable, less capable outcome.
Submarines aren't like normal items, like a car or a plane. We learned this with Oberon's, where mid life maintenance was ~75% cost of a new submarine. We also spent a lot of money developing a logistical support chain so we could actually fix them and make them operational. So it becomes cheaper/better to operate them if you build them here. It is extremely hard to operate a sub away from facilities and workers that can build and maintain them. Its like a lot of journalists seem to have never had any understanding of the last 60 years of submarines and Australia.