One possible arrangement of the light rail lines in Scarborough, connected to the subway extension.
Some great ideas. I think turning Sheppard into a high-floor, high capacity LRT would work well. In Ottawa the soon to open Confederation line is a grade seperated high capacity LRT. Maybe the existing Scarborough Centre SRT elevated station could be upgraded and incorporated as part of this line instead of demolishing a perfectly good structure. The station is already fully accessible and still young at 33 years old.
Sheppard gets converted to high-floor, high capacity LRT and goes to STC and then to Malvern, serving Centennial Progress campus en route.
Eglinton gets extended pas Kennedy all the way to UTSC (remaining low-floor).
Another service (let's call it Scarborough East LRT; low-floor) starts at Kennedy eastward, sharing the tracks with Eglinton till UTSC. Then it goes to Sheppard, turns west, connects to the Sheppard-Malvern line and shares tracks with it till STC.
It shouldn't be difficult to build a section, STC to Sheppard, shared by high-floor and low-floor trains. Known in a number of cities around the world. But if TTC is unwilling to do that, then the high-floor Sheppard line can end at STC. Malvern will be served by its own low-floor line (although the loss of through running is a bit of a disadvantage).
There are possibilities for Finch East LRT as well; I did not put them on this map to keep it simple.