From MP.net:

However, although the 13,000 Steyr rifles which have been in service for 20 years, would not be replaced, they would be a significant part of the upgrade programme.

The study would look at modifying about 3000 of the 13,000 5.56mm rifles so they could take more fittings on the top rail, instead of the factory-fitted 1.5 magnification sighting system

The Australians already use a mixture of the AUGs with 1.5x sights and the ‘railed’ AUGs. I have always thought that the 1.5x scope was a bad compromise on an assault rifle. The target acquisition speed is less than a non magnified red dot sight (I have no experience with magnified red dot sights) but lacks the benefits of a more powerful scope. It must be working for the New Zealanders because they are only thinking about converting 23% of their rifles.

Australian Solider in Iraq with ADI Austeyr A3 that
comes fitted with a rail.