Respectfully,I think you missed my point (or I didn't articulate it properly); an infrequent service, no matter how fast, will never be convienent because the odds of the trips times matching your activity are significantly lower.
If you have to find things to do, waiting for your transport, you're no better off.
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And I think there might still be a market for this service, even at one trip each way a day. I know many people who have to occasionally travel into Toronto, and they plan meetings with all the people they need to see, and fill up their day. It would be great to travel in 18 minutes instead of 2 hours.
I occasionally have to go to Bloor/Yonge for work. If company were to reimburse and the price were to drop to, say $75 O/W ($150 isn't much more than mileage and parking), I'd consider it. Sure beats leaving KW at 530am.
Usually frequency is more important than speed, I agree, but I agree with timc when he says "If it's worth spending $200 round trip to go to a meeting in downtown Toronto, you can probably schedule the meeting around the flight." As a relative grunt in my organization, I still have plenty of ability to organize meetings with clients around the train schedule from Kitchener. If you're spending hundreds to save an hour or so on the train that could still be productive, you likely have plenty of influence over meeting times.
I still doubt it makes sense here, and wouldn't imagine they would fill the plane too often. And, though I know this isn't a big consideration for many, the carbon footprint of flying ninety kilometres is significantly more than taking a car or train.