Northern Light
Superstar
Indeed!
And nothing stopping them completely changing their mind later. Recall the Green line in Montreal. Everyone keeps talking about Lionel-Groulx (the first station past Atwater) being so great.
But that was never the plan. Originally it was built on the assumption going to keep going west towards NDG. And then, they end up looping it 180 degrees to run east through Lionel Groulx, and then turn west again, in a big S-bend, actually going so far west, that it passes directly underneath Westmount High School.
On paper it looks like a horrific detour. But living there, it's not a big deal. And it works. Someone posted this above, but here it is again. Pretend you are a Montrealer, and west is actually southwest.
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I get your example; and you're not wrong insofar as Mike Harris filled in the tail tracks (tunnel) of a nascent Eglinton subway. Nothing is irrevocable that doesn't defy the laws of Physics.....or such.......
But........the SSE Station has already had the tunnel boring Machine pass through...........its not conceptual.......so barring one hell of reversal......