We do know that the Corridor doesn't really lose money though. And population growth has far outstripped whatever estimate was around when the Venture contract was signed. I should think that an extra car per train shouldn't result in a net loss, even with lower off-peak yields. 7 car trains might be a reach though. Heck, they could make the added car a business car and trade some business class yield for higher net. Akin to how airlines use business reward seats (yielding nothing) to keep up loyalty. End of the day, VIA One is competing with airlines only marginally. It's VIA Economy that is basically competing with bus lines, who might complain.
I do agree that with Alto on the horizon, it might be a harder sell. But even if these additional coaches are delivered by end 2027, we're talking about a decade of service before they are competing with Alto. More than enough time to at least pay off the capital cost.