If you look at Line 2, the distance from St. George station to Sheppard East in Scarborough is 22.0 km. The distance from there to Kipling is only 11.5 km. If you extended Line 2 from Kipling to Square One, along the CP tracks, and then up the long-proposed spur to Square One, that would be be another 10.5 km - making St. George to Square one 22.0 km.
St. George would be the exact middle of a Square One to Sheppard East Line 2 alignment. Which always makes me puzzle the reactions of some I've seen about how crazy far Square One is.
Also, many seem to forget, that a lot of riders get off at each stop at peak, not just downtown. I used to ride the Danforth subway for 4 stops as part of my regular commute. The changeover was huge. Sure, some are in it for the long haul. Many aren't.