Lets say that we build the Queen subway with stations spaced every 850 metres or so (that's roughly the distance from Yonge to Sherborne, so well within what we're used to). Most people will transfer onto the subway, as they will know that subway will be twice as fast as the Queen Car.
Once the construction is finished there won't be the ridership to justify rebuilding the streetcar tracks. Like Bloor-Danforth, there will be little need for a surface bus. If we build it using deep level tubes that don't disrupt the suface, the Queen car has 25 years left until the next track rebuild. At that point, the ridership won't justify rebuilding the streetcar tracks.
A political decision to run the service as a heritage line would be its only hope.
I'm not saying that a Queen subway is good or bad... I'm saying it can't coexist with a Queen streetcar. To preserve the Queen car, we'll have to build the stations greater than 1 km apart and I don't see that flying in downtown Toronto.
Even if you built stations 1k apart, not enough ridership to support the stations in too many places.
The Queen line would be long haul and bypass various points.
At the same time, if you got 2 good legs, walking is not a real issue. If you got a walker or need a cane to use to walk to the stop, it becomes a chore to get there in the first place. This gets total ignore by planners.
As I have said in the past, Spadina, Bathurst, Dufferin Roncesville, Yonge, Woodbine and University are the only real trip generators for a Queen line. Lansdowne, Coxwell, Pape, Broadview could be use as stops. To please the Beech area, you would need one at Nevile and one mid area. You could put a stop somewhere between Yonge and the Don and most likely be River St. it will service the West Donlands area that is being built now that will become a trip generator in time.
At the same time, you still need surface service to provide service in between the subway stops. I would still use streetcars as it will support the street better than what happen on the Danforth when the subway was built. It will maintain the Toronto history.
When it comes to rebuild Queen Street, move the tracks to the curb and kick the parking off it. Then there will most likely not that great number of them then in the first place.