I don't know why people are still fixated on the idea of the Southern Cross subway. I would have thought by now that its pretty clear it will never be reopened.
It isn't DDA compliant, which if they reopened it would mean they are breaching the DDA in a way that continued use since being built before DDA doesn't apply to.
The subway is used for other services now, that would have to be relocated somewhere else at great expense.
What is needed at Southern Cross is better quality escalators on all platforms, including V/Line, better way-finding signage, and ultimately more frequent, consistent services.