Seeing that the western half of SmartTrack has completely dissolved, with that section only having 10 min frequencies, I wonder if there is now a business case to be made for bringing the Relief Line to Mt. Dennis (Eglinton) or beyond, via Dundas West Station, as SmartTrack's replacement.
For the Relief Line terminating at Dundas West, the YRNS forecasted low/moderate usage of 11,000 pphpd for 2031. The SmartTrack report showed demand of 11,500 pphpd, approaching Dundas West Station from the
north, on SmartTrack including the western spur.
Obviously we can't directly compare these two reports with wildly different set of assumptions. But what this does show is that there is significant latent demand for a direct central west end to downtown rapid transit link. This is an idea that should explored in an official capacity in the relitavely near future, perhaps as soon as the completion of planning for the eastern Relief Line.
Also, tying the western Relief Line to a suburban subway could make the western RL easier to sell politically.
SmartTrack ridership forecasts:
http://www1.toronto.ca/City Of Toronto/City Managers Office/Intergovernmental Relations/Files/PDF/SmartTrack Ridership Forecasts Report.pdf
Yonge Relief Network Study:
http://www.metrolinx.com/en/docs/pdf/board_agenda/20150625/2015-06-25_Yonge_Relief_Network_Study.pdf
DRLNow has more info about a potential western Relief Line:
http://www.drlnow.ca/