I've actually looked into this further, Kitchener-Guelph are approx. 22 km away from each other. it takes 17 minutes to get from one to the other. and you need a loop in the middle - there's conveniently located GO owned grain elevator tracks. If you construct a switch from the mainline to the branch, and a track from the the 2nd grain track to the mainline so that it would still have access, you would have 15 minute service between Kitchener and Guelph.
@ARG1 the business case says a total cost of $150 million inc. for track upgrade and speed increases, but a lot of the work needed is already being done in projects like the Guelph south Platform and the ION. The true cost is probably lower. The BCR even in low growth hourly frequency scenarios is positive.