You need to realise that the Australian submarines will not just be conventionally powered versions of a nuclear powered Barracuda. The Barracuda is in effect a reference design, which Naval Group will use to inform the design of our subs. In practice, a grab bag of designs and techniques and equipment which will be used as building blocks. While the hull shape might be similar, it's likely to be smaller, and the arcane business of fluid dynamics and the need to fit everything that Australia demands will decide just how far it can be "pantographed down" and how far 1:1 scale water effects will require changes.
I am skeptical that the Australian submarine will be a pantographed down version of the Barracuda hull. Information from DCNS indicated that during the selection process, the proposal put forward was the same diameter and in length was stated approximately 1 meter shorter although it is unclear if that was due to any changes in the hull itself. Scaling up existing designs are fraught with huge difficulties, as we experienced with Collins. With Barracuda, or any engineering design, scaling down is almost impossible without essentially starting from scratch, and that is before any fluid performance is looked at.
There is also no reason why Australia would be looking at a specifically smaller hull volume than the existing Barracuda design. I don't know why people believe that would be the case. At no stage did DCNS propose a scaled design. It would be extremely beneficial to keep the volume and hull form extremely similar to the existing design. Neither did the Japanese. Australia's requirements are very significant and in some areas exceed existing SSN designs.
In other words,, we will still have significant FOC issues, and no-one but an incurable optimist could gainsay Murphy.
There will be significant issues with any new submarine, even of an existing class, from a proven and experienced yard.
However, there is hope Australia can improve on the currently expected 12 year build speed of the current first in class Barracuda submarine. Or the Brazillian build speed. The first subs of the Australian design is likely to be closer in design to french subs 5 and 6 than it will be to french sub 1. They will still be very different to the French SSN baracuda class, but they will base or benchmark the existing French hull and equipment from DCNS catalog. A catalog which is in development with many ongoing builds, including SSN and SSK designs. In addition, UK sensors, US systems and weapons, there is nothing stopping from Australia from selecting a Japanese, American or UK technology where it feels those would be more sensible than the French option if available.
It is quite likely the first in class will take longer than the desired drum beat. Then as often with manufacturing, production speed and efficiency can be improved.