I think what might make sense is an integrated ticket/presto charge with a maximum of $5, where the subsidy of a cross-boundary trip is roughly split equally between municipalities.
I don’t like it. Fares are already a tax on poor people or on people that can’t or shouldn’t drive, that rely on transit, while simultaneously dissuading those that choose between it or driving a car/ride share. Increasing fares does nothing but increase the burden and create more traffic.
What would make sense instead is finally have tolls up on the highways leading into Toronto and making transit free. The operating revenue is already only 1/6th of what the subsidy revenue is, and the surplus is equivalent to at least twelve years of operating revenue, so they could easily come up with an alternative way of generating income if the highway tolls don’t work out.