Might be able to fit a surface subway situation, similar to Allen Rd, between Sheppard and York Mills (36 metre right of way on Don Mills). South of there must be grade separated. Remember that the pillars for elevation take up road space, perhaps as much space as a surface LRT. Realistically, underground is the only option for Don Mills. Planners and residents will be none to pleased with disrupting a stable residential neighbourhood with elevated subway.