Business case is that trains to/from vic can be double stacked and be 1.8km long, and they don't need to traverse the Adelaide Hills.
This benefit has been studied before and it didn't stack up (pun intended) when it was included in the business cases. Firstly, there are a number of overbridges that don't have double-stack clearance on the Geelong-Ballarat-Mildura corridor, particularly between Geelong and out just past Ballarat, so they have to be tacked on to the project to achieve double-stack-compatible clearances for the entire route. Not a huge extra cost, but it adds up.
Second, the disbenefits of not going to Adelaide are too great for most freight services (PN & SCT have busy yards in Adelaide). What happens these days instead is that the well wagons used for double-stack container traffic come from Melbourne with a single stack of containers on them and the Adelaide loading is put on top to make a double-stacked load. Once the Inland Railway is finally built the benefits will be even more marginal, as Melbourne-Perth loadings could be hooked on to Melbourne-Brisbane services at transferred to the East-West line at Parkes - on 1800m long double-stacked trains, no less.
Reopening the Pinnaroo line and standardising the last remaining broad gauge section would be a far better move. Mildura would get relatively direct access to the Adelaide-Darwin rail corridor AND to Port Adelaide.
It'd be nicer still if Viterra actually wanted to use the Pinnaroo line to cart grain, but that doesn't look like it's going to happen so the idea is a non-starter.
Maybe this push is just an ambit claim designed to make the Pinnaroo option look better?
I'd be more worried about whether Jason knew what an ambit claim was before asking whether he's the sort of five-dimensional chessmaster that tries to pull off that sort of trick.
More sense would be an east west connection to Hay and Port Augusta ish. Better freight connection to key markets in Sydney, Adelaide and Perth (Brisbane too).
In my opinion one of the great 'what-ifs' of 20th century Australian railway history is whether the Commonwealth should've extended the Hay line to Wentworth, Morgan and thenceforth to Crystal Brook as part of the East-West corridor. It would've been a high-cost but high-benefit line for the region but of course it was also total political anathema for NSW and Victoria as all the benefits would go to Adelaide with it then becoming the closest port city.
Perhaps if SA had somehow moved its borders say 50km eastward to include Broken Hill then we mightn't be discussing this as a hypothetical...