The better not do the "loop" plan at McCowan Station. Then the subway would goInterlline with the York U extension and you have a my vote. The final route would be VMC to STC
From Vaughan to Sheppard, around the loop to STC, to Kipling.
The interlined one would go From Vaughan down to Union and up to Finch.
Having only 2 very long lines seems hard to run.
I had a plan for this a few years ago. It could be fit in, and the best part is the bulk of the construction for the various interchange ramp to accomplish this would be built on airport lands.This works! Alternate trains going downtown and to Scarborough at Sheppard West as well, would help traffic flow on Yonge University.