I've always felt Scarberian was pretty knowledgeable about Scarborough (or maybe I'm just influenced by his username).
If I were to trust two people to come up with a new subway alignment from Kennedy to STC, I'd trust scarberiankhatru and keithz.
And when it comes to things like exact alignments, I'll defer to Scarberian.
It's funny to see some folks who've left Scarborough argue against extending the BD line to STC. You'd be hard pressed to find any Scarborough resident actually saying they'd rather get LRTs on Sheppard and from STC to Sheppard/Progress, over a subway connection to STC.