I still can't wrap my head around why some people seem to think it is as easy as flipping a switch to make the Eglinton LRT line into full-bore subway.
Aside from the fact you would be taking away higher order transit from thousands of people beyond the central tunneled portion (unless you've magically discovered billions of dollars to trench/tunnel/elevate the subway line the full extent of the existing planned LRT line), you've got significant additional costs.
Where are you going to store your new subway cars? The LRT plan has a yard out at Black Creek. The advantage of surface running LRT is that you can access the yard just by turning north (see panel 28
http://www.toronto.ca/involved/proj...n_lrt/pdf/2009-11-20_display_panels_part2.pdf).
If you build a subway, you can't pop out of the portal on the side of the hill and then cut across traffic, you'd probably need to tunnel (or some wacky elevated contraption that would be an eyesore and need copious amounts of space just to drop back down to grade in the yard). So now you are coming down the steep hill from Keele (very deep tunnel) and must continue tunneling down and UNDER the watercourse while making the right turn to get into the yard. (And is the proposed yard big enough to handle the full subway cars? Or are you going to have to spend hundreds of millions more to figure out some kind of connection with the YUS line so you access Davisville or Wilson (neither of which will have any available space once the Spadina extension comes on line)?)
On the eastern end, either you end your line at the portal (and give rise to the transfer problem covered below) or you spend hundreds of millions more to either tunnel all the way under the Don Valley and right through to Don Mills, or to build some kind of grade separation along the south side of Eglinton (which is not actually at grade down in the park).
Presuming you can't find the money to extend the line as far as the current proposal, or even as far as Don Mills, you've now got to spend millions on some kind of station at both ends where all the bus routes feeding the line can come and drop off passengers. Anywhere around the eastern portal you can easily build this? There are a lot of bus routes (and corresponding passengers) you need to accommodate.
Or you can stick with the plan that is currently funded, provide a true cross-town route with a central portion in a tunnel that will provide near-subway service. (Also worth noting you can't really be carrying more people than LRT capacity because you've got nowhere for them to go - YUS is already maxed out and additional capacity provided by Toronto Rockets and ATO will be quickly consumed north of Eglinton.)
So all in all, people advocating converting Eglinton to a full heavy subway seem to want to spend billions more dollars for negligible or even less benefit (if they are taking away better transit from the non-tunneled portion). And then they'll saddle the Toronto taxpayer with all the costs of starting over the design, environmental assessments, the endless public and private consultations, the breaking of existing contracts, and throwing away all the money already spent on the line. That sounds like complete disrespect of the taxpayer and a guaranteed gravy train.