I can think of two specific use cases for people using an ION park and ride at Sportsworld: First, those headed to the GTA from Waterloo Region by bus. Second, regular commuters from Cambridge who either pay for parking in the Downtowns or large institutions on the line. If you're driving all the way from Toronto you're probably driving directly to your destination at that point. This could be further sweetened by employers who offer discounted passes or parking cash-out. You're right that traffic congestion in the downtown isn't there yet, but give it 10 years. It's a carrot-stick thing, governments typically do better with the carrot.
Main point though is that ending the line at a Transit Hub by the 401 isn't the worst option for phase 2 if Cambridge can't make up their mind.
Main point though is that ending the line at a Transit Hub by the 401 isn't the worst option for phase 2 if Cambridge can't make up their mind.