The building of the lines are based on ridership and density as well long range. Been flip flopping on a few
Burnhamthrope with an issue to connect to Islington or Kipling,
I can see Eglinton Crosstown Line ending up at Square One.
Hurontario is under construction already.
Eglinton looks like a good next candidate. With Eg West being tunneled / elevated between Mt Dennis and Renforth, it will be overbuilt for its original scope. But if it gets another branch running into Mississauga, then the tunnel kind of makes sense for the combined high frequency of the two branches.