I expect that for the reason you mention it's improbable the US or UK could do a full build for Australia even if it wanted it. Maybe the first of class could be completed overseas and the rest assembled in Australia?Politically, I think a partial build in Australia would be essential. I think it would also necessary from a capacity POV as well. Columbia and Dreadnaught will be stretching US and UK resources.
Still this is very interesting news. If Australia is willing to spend the big bucks to get an SSN it would be very valuable. Plus the French design seemed really problematic and expensive for what was still a conventional submarine.