Sydney has 3 runways that seem to function as 2 runways 99% of the time.
The big difference is that Melbourne has 2 runways, which seem to function as 1 runway quite often. That’s when the holding happens.
The holding advisory doesn’t change when Melbourne is likely to be running single runway. A pilot familiar with the Melbourne single runway issues can look at the forecast winds and predict this, but not all pilots have this local knowledge. In fact even the forecast winds are not necessarily a good predictor, as pilots only get the average forecast wind directon, not the variation, and a variation of above 5TW on 27 closes the duty runway.
Is it likely to help when/if a 09/27 parallel opens? Or will the third runway be hampered by the same issues as the existing 09/27? (i.e. south-easterly component continuing to reduce the airport to single runways? Or will it open a 09 option? Or course a strong northerly will still be a problem.)