So there are no plans to go west of Yonge?
The priorities are, in order:
1. Relieve Yonge and Bloor Stations, as well as the East Downtown subway lines (Union-Bloor of the Yonge line, Bloor line from Bloor Yonge to Broadview)
2. Relieve the downtown streetcar network, particularly the King streetcar
3. Relieve the Yonge line in its entirety, allowing for future extensions of that line
4. Bring development east of downtown and yonge street in general
5. Relieving St George & spadina stations, as well as the west downtown subway lines (University Line, Bloor Line from Dundas West to Bay)
6. Relieving the 501, 504, 510, 511, 505 in areas where crowding isn't a huge issue.
As you can see, priorities 1, 2 and part of 4 are taken care of by Relief line East. 3 & 4 are from relief line north, and 5 & 6 are relief line west. All in all, the priorities of the ttc are being addressed by building relief line south first, followed by relief line north and, if demand is ever reached, relief line west.