Methinks extending the subway to Scarborough Centre along an entirely different route than that of the SRT would be serving brand new areas of the city that before have had to contend with endless congestion and gridlock during rush hour. New stations at Brimley/Eglinton and McCowan/Lawrence would head off the brunt of bus traffic coming inwards from the desnely populated Morningside-West Hill and Cedarbrae-Woburn communities respectively. About as much, if not more people than all of Malvern. So don't think of it as robbing from Peter, or from anyone; you'd be catering to more commuters! One plan calls for the ill-conceived Kennedy Stn locale to be transformed into a permanent lasting hub where 3 LRT lines will intersect with the subway, when there is little particular demand by the majority of Scarbrough commuters to spend any time there. Interregional buses feed into SCC, not Kennedy, so if one's coming in from Markham or Pickering they'll now be forced to transfer twice just to get to the Bloor Line. Madness. We already have one LRT line going to Sheppard-Progress, remember. We don't need another when all it will do is produce out-of-the-way transfer points that very few will want let alone prefer to connect through a lot like McCowan RT Stn in relation to the main hub that's just across the way.
I don't even see why a simple cut-and-cover stacked tunnel method couldn't be applied down McCowan-Danforth which is 6-lanes wide with lots of lawn frontage surrounding it the whole length. Such construction method could even allow for 2 driving lanes to remain open during the construction period which I assume would be expedited.