QR taking a 25% stake in VA would be an ownership change. If ownership of an Australian airline becomes such that it can no longer be considered to be an "Australian" airline, they no longer have access to capacity applications from IASC.
QR using part ownership of VA to access the Australian half of the Australia-Doha capacity, especially when using their own aircraft under a VA code, would be a clear attempt to get around the Air Service Agreement limits.
IASC is a part of the Department of Infrastructure, Transport, Regional Development, Communications and the Arts and Policy Statements issued by the minister form part of the criteria used when allocating capacity.