NOTE: I am not a daily Sheppard Subway user, nor have ever been, however, I have experienced it quite a bit as I have friends that live near Leslie Station.
It is estimated that the Bloor Danforth line may require a higher subsidy (if any subsidy) per rider than the Sheppard line, especially when one considers that the line is much older and requires more maintenance, the trains are longer and require more power, more crew are necessary to support the line, and that 300,000 of the 500,000 daily users transfer from the BD line to the Yonge line. (I went over this in another thread). The point is that either all subway lines receive a subsidy, or no lines receive a subsidy (or barely any subsidy, including Sheppard).
Also, even now the Sheppard subway looks pretty busy; at least similar to what all the other subway lines look like midday. Crush loads? Only during failures. Standing room only? Very often during rush hours, and occasionally early evenings (The Sheppard subway is interesting because some days it's empty, and other days it's standing room only. It really depends on how many people are going downtown at the given time. Some Fridays can be painful, others plenty of room). Finally, we have to consider that the Sheppard Subway actually carries a lot of people: 50,000 daily. Considering that the line is 5.5 km, the line carries more passengers than the PATCO Speedline in Philadelphia, the Cleveland Subway, The San Juan Subway, The Baltimore Subway, The Staten Island Railroad and almost as much as the Miami, Pittsburg, Seattle, etc subways IN THEIR ENTIRETY. Going by route length, the Sheppard subway carries more or near the number of passengers per km than the Subway Lines of Philadelphia, Boston, Chicago, San Francisco (Excluding MUNI), Washington DC, London (More: Metropolitan, Picadilly, District, Around: Central, H&C, W&C), Copenhagen, Stockholm, Berlin, Helsinki, Hamburg, Milan, and comes somewhat close to Shanghai. (Again, those are system averages (daily ridership/length of system (km)). Calling the subway a white elephant is a little bit ignorant (it's not as great compared to the YUS line, BD line, but it is certainly not unreasonable).