I agree with this map from Roncesvalles to Eginton at Don Mills. I just have never been convinced that a subway needs to get to Dundas West. The Roncesvalles streetcar doesn't seem that busy, High Park isn't a huge trip generator, and the areas east of the park have good access to downtown. I see High Park and Humber Bay as the eventual bottle neck to east-west movement that needs relief (southern Etobicoke is relatively underdeveloped currently for an area so close to downtown) so I think that before heading north a subway should at least reach Humber Loop to capture all the east-west traffic south of Bloor. Currently many head north on various bus routes to Bloor subway to get past the park, and then come south again. The Queen car and route 80 are the only local services south of Bloor. Also, running a subway along a rail corridor for an extended distance doesn't make sense when you can run GO REX EMUs in the rail corridor at high frequency and achieve the same benefit and simplify operations in the rail corridor by having compatible rolling stock.
Imagine REX stops at Union, Dufferin, Eglinton,and Calendonia (as shown in the map) plus Earlscort which has been seen in plans, plus Weston which is off the map.... what new area does a subway up the rail corridor serve? Stated a different way if you are standing at the platform at Mt.Dennis and the subway pulls in and the REX pulls in, besides the subway going slower there are only 3 or 4 stations of difference. If we are going to build subway it should be relieving services that are at capacity (I don't see the Georgetown corridor's 4 railway tracks as being anywhere near capacity) and opening up new and faster routes to currently under-serviced or congested areas. I would propose having the DRL's west side continue to Royal York and Queensway, then take the most direct diagonal line to the airport terminal crossing under the runway. From a connectivity perspective it adds GO Kipling & Bloor Line, Renforth BRT, and the airport, it provides a completely new transportation corridor servicing the whole southern part of Etobicoke (improved connection to Lakeshore West LRT, Queensway, Six Points redevelopment, East Mall / West Mall developments, and the Airport Corporate Centre's large job base.