I included just the two pics above to answer your very good post, as what jumps off the page in astounding logic for me is:
Surface Run the QQELRT.
Tunnelling where unnecessary is an absurdity. What resonates in my mind, other than the filthy snow and line of cars, is the San Diego Convention Center with the SD Trolleys running in their
surface RoW proudly in front of the building:
Obviously San Diego had the sense to retain some class to their boulevards, and those boulevards and streets are much wider than QQ, but note also the
railway mainline to the right of the LRT tracks. That goes to the freight and commuter train yard to the south of this picture and onto Mexico, as does the LRT. In fact the mainline and LRT share that trackage, a whole other point that Ontario might wish to consider...next century. Maybe...
Instead of burying everything, ostensibly all for the sake of the Almighty Car, just bury where absolutely necessary for ease of streetcar flow. It might even be wise to consider filling in the ramp from the western portal such that east and west QQ lines join head-on and a surface 'Y' is built such that the stem of the 'Y' feeds into an emerging portal at the base of Bay St. Surface streetcar congestion? Perhaps. They have computerized signalling and control in other cities for such things to smooth and dynamically adjust speeds of approach and timing, and thus maximize throughput.
If that plan has too many detriments, then surface-run the streetcars for QQE into a portal to run into another tunnel to the east of Bay leaving the present Spadina loop intact and as is save for increased passenger loading/unloading space at Union. Or as some have suggested, use double-ended consists that reverse in stub tracks near Union with a separate entrance altogether than the Spadina leg.
As if Toronto isn't in enough knots as it is through piss poor planning, lack of vision and penny-wise pound foolishness. And now Rube Goldberg becomes the inspiration for City Planners on this matter.
ULTIMATE Rube Goldberg machine - YouTube
There's still time to do a loop to the east of Bay. And burying it under QQ for the length proposed just makes the concept that much more impossible in rational terms.