This came as a surprise, The Sheppard Finch BCA
http://www.metrolinx.com/Docs/general/Sheppard-Finch_BCA_Report.pdf
There are five options presented, one is including converting the subway, and another is extending it, but only to downsview
Nice way to stack the deck by not including the option of extending the Sheppard Subway in both directions. A fairer comparison would have involved studying expanding Sheppard to Downsview and to STC at the same time, for a nice long continuous line that would have helped riders in the east and west. It's a very political omission, obviously.
The cost to shutdown the Sheppard subway for option 2 (converting Sheppard subway to LRT) is $670 million. I'm not sure what that includes, but that's an obscene amount to reduce capacity in my opinion. Comparing that to extending the subway to Downsview, you might as well extend the subway to Downsview versus converting Sheppard since it's $3.65 billion versus $3.59 billion.
Not surprisingly, the subway to Downsview has the highest development potential (2.3-6.0 billion), the best land use shaping (but not "priority neighborhoods" whatever that means (cough, Malvern, cough)
This quotation is interesting: "Option 4, which has the lowest effect, will reduce GHG emissions by some 25,000 tonnes in 2021. The reason for the lower GHG emission reduction under Option 4 is due to less constrained road space. In Option 3, road capacity will be reduced for a longer distance and will have a more significant effect on drivers."
As in, they view the bad effects on drivers as a good thing.
At the very least, option 3 doesn't preclude extending Sheppard to Downsview, unlike options 2 and 5. I still don't like the Sheppard East LRT, but some of the other options they examined were even less palatable.