Line 4 extn... I think it *could* happen, provided that our planners are more open to options between a 6-car deep bore subway and in-median LRT. But they're not. So yeah, as it stands Scarb will be even more "remote" with SSE than with Line 3 plans. And by "plans" I'm including the simpler upgrade that preceded SLRT. History didn't begin in the late 2000s, so can't ignore viable options before that period.
In many ways, I honestly think the line 4 extensions east and west could have been better for Scarborough than a line 2 extension, though we don't know the true costs so it's very difficult to make a fair argument, but as it goes:
-There would be fewer stations, so dwell times wouldn't be as bad (Especially with RLN coming), meaning trips could be faster
-The line would see more utilization and potentially become busier
-The line would provide Scarborough with 4 ways to get downtown: Via Sheppard Subway and Relief Line, Via Sheppard Subway and Yonge Line, Via Sheppard Subway and Spadina Line, Via Eglinton Crosstown and Lines 1 (Y), 1 (U/S), 2, 3 (RL). With this setup, you could get almost anywhere in the city with only 0-1 seamless rapid transit transfers (Uptown, Midtown, Downtown, East York, Etobicoke, Vaughan, York University, and eventually Richmond Hill and potentially Mississauga)
-The line uses shorter trains and runs with slightly longer headways, but all this can be upgraded with ease if future demand persists.
-The shorter trains will save money on electricity costs, as well as maintenance. The line is also newer in general, so it won't cause as much wear on existing stations.
-There would be more rapid transit stations in Scarborough (LRT that isn't fully grade separated is not "rapid transit", but it is most certainly higher capacity, higher order transit)
-Sheppard connectivity to Wilson Yard and Line 1 (Y) direct connection to Wilson yard. The availability to store trains there and turn trains around Via Sheppard would do wonders for the city's rush hour issues.
-Less deadheading when trains go out of service and enter service
-Would keep Scarborough commuters off busy lines like the Danforth line (the 3rd busiest line and approaching a choke point if I'm not mistaken after Yonge and University)
-Can utilize OPTO which would save millions annually for the TTC
-People would transfer at Sheppard Yonge, Sheppard West, or Sheppard-Don, and not at Bloor-Yonge/St George, meaning fewer people on those platforms and potentially saving lives
-Opens up possibilities for a new subway rail yard, maybe even for RLN.
So now that that's settled, sounds we debate the merits of a line 2 extension to Sherway
Well, since the Milton line is the most crowded GO line and will barely be upgraded, and with so many people taking the QEW to Gardiner entering Toronto on a daily basis, that in itself can serve as a fair argument for any westward line 2 extension.