Yes, the line is dual gauge, though the broad gauge rail is disused and I don't know if it's intact over the entire length of the line.
AIUI the former passenger service detoured via Rosewater, and ran to GMH Elizabeth.
Alas with the PREXY parallelling it, I'd expect there to be even less demand for it now than when regular services ceased. But I do think there's great potential for a bus link via Cormack Road to link Port Adelaide, Gillman, Wingfield and Dry Creek station... and possibly also Mawson Lakes.
And in the very long term I'd like to see a monorail running alongside that line and on to TTP via Northfield.
Just build it wrote:Bye Union Hall. I'll see you in another life, when we are both cats.