I have suggested just this, publicly, and here on UT, in the past.
The logic goes something like this:
1) The rails and corridor are fully in place here, and the cost of upgrades, station aside, is lower.
2) It serves existing local demand, reducing transit/driving distances to Allandale for some commuters.
3) The investment is on a portion of rail that retains some active freight uses, and the upgrades could assist in better serving those needs incidentally.
4) Reduces the future project cost of any project to restore rail to Collingwood/Wasaga, by knocking off a 2-3km section, and by increasing the potential number of customers/interest in the longer term.
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@ShonTron is entirely correct that the first step is boosting Linx to 7-day service and evening service in all corridors. The number of growth of potential customers and proof-of-concept are essential foundation works for major rail investments later.
But I do think the one-stop extension merits serious examination.