Australia, inland route, Melbourne-Brisbane

https://inlandrail.artc.com.au/" onclick="window.open(this.href);return false;
A big scale project, thats been talked about for years.
Personally , I don't know why they don't start a service on the existing tracks, with road bridging for the 500 or so missing k's.

I think the failure to build a more direct and shorter route was probably a result of the adoption of the Irish gauge in Victoria.

The standard gauge link has been in place form the NSW border to Melbourne since the 70's.
Gauge wise , I think the Brisbane end is the biggest problem, with a long stretch of narrow gauge. I haven't read far enough to see if they will convert it to Standard gauge , or build a new standard gauge line. The map gives the impression it will be a new standard gauge line in a more direct alignment.

I have taken the train from Sydney to Melbourne and returned. I assume that a direct connection between Melbourne and Brisbane could be quicker than going via Sydney. But would there be enough traffic to justify it?

If it took some of the traffic of road , yes , I think there would be . By all reports, There are huge numbers of trucks on these routes.