I am not betting on ridership being low. I'm visiting someone that moved to Vancouver who hasn't taken a bus once, but takes the SkyTrain daily. I took the bus once yesterday, but I'll stick to the train or walk/bike now.
I think trains have more potential riders than busses due to preferences, from classism, comfort, predictability, frequency, etc.
One thing I noticed about the SkyTrain, is that it doesn't offer more coverage than Edmonton's system will in 2027, but it goes to every place that I'd ever want to go. If something isn't along the SkyTrain, or within walking distance, I'm probably not going there. Also, the SkyTrain is surprisingly slow. I prefer Edmonton's subway portion, it feels more New York.
The big ridership boost is absolutely going to be the West line. Opening up West Ed to young people along the entire line.
But do not underestimate young people's hatred for driving.