You originally stated in your photo post:
And again, we have seen that just because planners don't currently envision the need for a transportation corridor doesn't make it unneeded. The city saw "no need ever" for the Richview corridor, and now we're wishing they hadn't sold it off. GO and the city saw "no need ever" for the Leaside spur, and now we're wishing they hadn't converted it to a trail. No one saw any need for dedicated tracks for GO along the Milton corridor back before Mississauga got built up (when a corridor would have been cheap to assemble), but now we're faced with a situation which will be very expensive to resolve.
Like I said, the Barrie corridor could actually be a decent spot for a local LRT, offering rapid transit along that corridor within Toronto (letting GO just focus on the long distance trips). The surroundings are primarily residential and connections to other rapid transit are good. My point being that it's not actually hard to envision a future use for the corridor. Just because there isn't anything currently envisioned doesn't mean there aren't any ideas that make sense now or will at some point in the future.
Once transportation corridors are lost, it's usually impossible to get them back. And we're really, really bad a preserving transportation corridors here in the GTA.