I think the UPX should have always been GO-RER from the get-go, but obviously we would be sans airport train right now if that was the case. We are looking at 2025 for GO-RER so we will still get 6 more years minimum out of the system. That being said, I believe the most expensive part was the airport spur; as long as they reuse this with GO-RER trains then its not a total wash. The spur had to be built to mainline standards, as is the rule by Transport Canada for using the UPX on a mainline, so it should support the weight of a double decker EMU. The Pearson station might have to be modified a bit. Perhaps we can buy some dual level boarding trains for the Kitchener Line, like Caltrain has
and the high platforms can be maintained at the UPX stations. The current trains can be easily sold to SMART in California.
Modifications would have to be made to Pearson station, but I think this is the best option.