I certainly concur that dedicated passing tracks are not coming to every GO station in the system, or even most, in the near to medium term. But I think its reasonable enough to imagine that can come to more stations, and strategic choices may be deliverable and inordinately beneficial, indeed for reasons other than passenger safety as well.
All recent station designs I've seen have included space for either a passing track (Downsview Park, Rutherford, Maple, etc.) or a gauntlet track on one side (Milliken, Agincourt, etc.). This is purely to accommodate wide freight trains once the platforms are raised for level boarding. Express trains would not necessarily use the passing track, and would definitely not use the gauntlet track since it would be designed for a low speed.
A simpler but very constraining patch would be to impose speed restrictions on every non stopping train at platforms.... but that would wreak havoc on scheduling and dispatching.
My understanding is that they've already implemented speed restrictions on the platform tracks at Exhibition due to it regularly exceeding the recommended crowding levels. That's one of only two station in the network that already have two express tracks without platforms, though construction is already underway to add platforms on those tracks. For the record, the other station with two express tracks is Etobicoke North. Its replacement station is also planned to have platforms on all tracks.
Humber Bay (Park Lawn) station is planned to have side platforms with two express tracks in the centre. I've always thought that this same arrangment should have been included in Long Branch station's current upgrade works, instead of having platforms on the express track even though express trains don't stop at Long Branch.
How I would have rebuilt Long Branch: (Existing platform in grey, new south platform in beige)
Some are wooden, and nobody responds well to being corrected, but some are real people people.....and as someone who spends their Saturdays (as a volunteer) asking people to stand behind a yellow line, there is nothing like a smile and a personal connection to get someone's attention.
I think part of the issue is that the yellow line is too close for full-speed trains. I was at Rouge Hill and a parent was telling their kid to stay behind the yellow line, and I commented that they shouldn't even be getting close to the yellow line let alone crossing it, since I knew there was going to be an express train passing through in a few minutes. Sure enough they were figuratively blown away by how fast that train passed through (it was around 130 km/h) and the strong winds that accompanied it. Long Branch is even faster - in the absence of construction trains regularly blast through there at 150 km/h.
Here's a clip of an express train going 148 km/h through Appleby station, just imagine if you were standing right next to the yellow line:
While waiting for a train at Baie D'Urfé Exo station a couple weeks ago there was a guy on his phone right next to the tracks (but still outside of the yellow line) so I told him 'attention le train arrive' and he just looked at me and rolled his eyes, before staring back at his phone as the train pulled in maybe 50 cm in front of his nose. Though he was outside of the yellow line, he was easily close enough to make locomotive's operator nervous.