In the process of designing a new subway line or extention, they discuss potential stops such as they did with Yonge extention north of Eglinton to Finch and most of these midpoint stops (Glencarin, Yonge Blvd - Glen Echo, Empress - North York Centre) never see the light of day again since the forcast for low ridership and lack of intersecting arterial road. These midway stops generally don't go beyond simple talk, there's usually never any planning, design or engineering work on these stations,... except,.... and as you can see from that article,... "This extension to the North Yonge extension would feature one station at Finch Avenue, despite lobbying from North York that a second station be constructed at Park Home Avenue (the Empress station referred to before, and the site of the proposed North York Civic Centre). Although a level section was designed into the line at this point, where a station could be added, the TTC would refuse the request to build this station until the mid 1980s, when construction began on North York Centre station." In addition, at that point the tunnel was also built so that subway platforms could be placed there later on. When North York City Centre (2 office towers, hotel, library, retail-office podium, etc,..) got built, North York City Centre station (aka at Empress / ParkHome) got built at developer's cost.
North York Centre subway station is the busiest subway station in Toronto without a direct bus or streetcar connection; ridership is based only on local walk-in from the area offices and condo towers. This area have changed greatly from the 1960s when the Yonge subway extention was proposed to mid-1980s (when North York Centre subway station was added) when area was already undergoing urban intensification being championed by Mel Lastman. (Sadly, the most famous politician from Yonge-Blythwood/Glencarin and Yonge-YongeBlvd/GlenEcho area was flip-flopping Karen Stintz who's political career was always guided by her own self interest at the cost of her local constituents.)
Also, if you compare the built-form of Yonge-Blythwood/Glencarin and Yonge-YongeBlvd/GlenEcho area from 1960s when these midpoint subway stops were discussed to today,... 99% of the buildings and houses that were there in 1960s are still there today! Same density, same everything,... only major change at these areas are new SportingLife store,... and GlenEcho North Toronto stop became a Loblaws,... oh, and more front lawns paved over for car parking spaces! So this is probably one of the few times the TTC did something right,... by not putting subway station or provision for one at these locations.
Besides North York Centre (Empress/ParkHome) Willowdale Avenue on the Sheppard Stubway line is the only other potential station that can be added to an existing subway line that I can think of off the top of my head. (Anyone know of any other?) It was considered during planning for Sheppard Stubway line but rejected due to some community opposition, low ridership prediction and shoe-string budget due to Mike Harris cuts. But provisions where built on the Sheppard Stubway line at Willowdale Avenue to allow for a future subway station.
The problem with Blythwood/Glencarin proposal on Yonge line is no provision was ever made for a station there,... the stretch of subway track there is NOT level. A subway station platform needs about 500 feet of level subway track otherwise the subway could accidentally roll when loading or unloading passengers. In addition, the tunnel support system must allow subway platforms to be added.
Is it possible to still add a subway station at Blythwood/Glencarin on the Yonge line? Anything is possible if you have a bottomless pit full of money! They would need to rebuild that tunnel to level both tracks and cut and cover requiring closing down Yonge Street road traffic along with shutting down that stretch of the Yonge Subway line for the duration of construction (how long did Union Station take to add just 1 platform without any track work?). Sure, this all makes sense so a handfull of people can cut a few minute from their walk to the closest subway station. There are many people in Toronto who would kill to get a 10 minute walk from their house to a subway station.
Its best to have these folks walk to Eglinton Station,... there'll be nice new buildings at 3 of the 4 corners,... and if they ever figure out what to do with the old Eglinton bus terminal, it'll be new towers at all 4 corners! The challenge is desiging good pedestrian flow from street level to subway,... sounds simple but city planning and TTC isn't known for getting these simple things done right.