It was mentioned in the other thread (which should probably be merged into this one), that it may be a possibility to purchase a few DMUs and run them along the Stouffville line between Kennedy and Agincourt (probably adding in some temporary stations at Lawrence and Ellesmere).
The capital cost of purchasing a few DMUs and the operational cost of running the service for 4 years would probably be less than the operating cost of running buses every 2 minutes during peak in order to meet demand.
Just to confirm, GO owns the Stouffville line right? Or at least the section inside of Toronto?