@TigerMaster: I like your map, it is another viable configuration of rapid transit lines in the western half of the city.
However, I do not expect the ridership of the single diagonal line to be that dramatically high:
Dufferin's local demand is not that high by the subway standards. That demand only looks huge because it is currently served by buses and those buses have to run at a crazy frequency. But if you go to the pphpd counts: say a bus (70 nominal load) every 1 min (60 per hour), would be just 4,200 pphpd, peanuts for any rail line. A better transit would bring higher ridership, but I don't see it going to more than 7,000 pphpd or so.
Same goes for any other local segment, say Jane north, or Kipling north in Etobicoke. TTC has no transit line that isn't downtown-bound and clocks anywhere close to 10,000 pphpd; Eglinton will be first such line, and even then the current forecasts are under 8,000 pphpd for the first couple of decades.
Now, the downtown segment will be the main driver of ridership, working in the same manner as Yonge / Spadina / Bloor / Danforth. A busy downtown section where lots of riders want to go, plus long outer sections working as collectors. The total ridership will be very decent, but I don't see it dramatically higher than for the existing lines. It should beat the Spadina branch, but probably not Yonge.
If an exceptionally high latent demand for that diagonal line existed today, most of those riders would be taking the Spadina line or Bloor line, and overwhelm those; something we do not observe. Of course, there is an induced demand and the impact of population growth, it won't be just the same riders redistributed between more lines. But, given that 2 lines serving the north-western segment are doing OK today, I don't think 3 lines will have troubles meeting the demand in the next 20-30 years.