For a similar service from Bloor/Dundas, the ridership, both diverted and incremental, seems likely to be lower, perhaps half as much, because trains on the University line are not as close to capacity as those on the Yonge line, and the interchange at St George is less crowded. Congestion relief benefits will be less, but time savings benefits to those who transfer will be greater, as the interchange walk distance is shorter. Metrolinx is already upgrading the interchange as part of the Union Pearson Express service, so capital costs would be lower. The distance to Union Station is also less, so there may be slightly lower O&M costs. The scheme seems to be just worthwhile, but there would be no incremental revenue to TTC or to GO.
Incremental O&M costs from Kipling and Kennedy subway stations are significantly higher, as the distance is further, but the time saving is also much greater, about 20 minutes, worth $3 to $5 to the typical passenger, and auto user benefits are also likely to be higher. However, incremental ridership is probably much lower because many passengers are already using GO, even given the $5 fare.
One solution would be to use PRESTO to levy a $2 surcharge to TTC passengers transferring onto GO, capturing half of the benefit. In effect the TTC feeder service, most likely a bus, would be "free." Passengers who drive to the station would continue to pay $5, and might also be charged for parking. Some passengers currently paying a $3 TTC fare and a $5 GO fare would benefit from a price cut, although these numbers may be fairly small. TTC would also benefit from additional revenue from people filling empty space on trains on the Bloor line. On this basis, the additional service from Kennedy-Eglinton seems worth exploring as a possibility, but probably not the Kipling-Bloor service.
Metrolinx has now apparently appointed consultants to examine this type of solution, but the Danforth-Main linkage, despite its obvious advantages, has not yet been analysed.