Why Australian cruiser capacity did not extend to battlecruisers

Could Australia have built five battlecruisers during the interwar period?

No. Australia could plausibly grow from light cruisers toward County-class construction, but battlecruisers required a different scale of industrial capacity.

Australia had built light cruisers and could plausibly have expanded its infrastructure to construct County-class cruisers. The investment already going into Australian industry made that a credible next step. Building five battlecruisers would have demanded a much larger scale of facilities. Cruiser-building potential therefore did not establish an immediate ability to construct capital ships.