I maintain a TTC transfer collection - in fact I've been collecting for around a year and a half now, almost as long as I have been a regular user of the system, and my goal is to eventually collect a transfer from each subway and RT station. Back in January I had a dentist appointment on Sheppard in Scarborough and took the 190 to Don Mills so I could take the subway downtown for the day. Along the way I got off at Bessarion so that I could collect a transfer from there.
Suffice it to say, heading up to the cavernous empty mezzanine, taking a transfer, and then returning to platform level alone - all the while feeling the collector's eyes boring in the back of my skull - was a slightly awkward experience
I can't see a subway extension on Sheppard being viable. Even if the capital costs were put up by various levels of government for an extension eastward to replace the LRT, it would cost Toronto unreasonable amounts of money to operate the damn thing each year at such a considerable loss. If it were up to me I would bite the bullet now and convert the subway tunnel for LRT so that it could serve as an underground segment of a combined Sheppard East - Sheppard tunnel - Sheppard extension to Downsview - interline with Finch West route, providing one seamless LRT line across northern Metro, but the costs there too are almost entirely prohibitive.
Building the stubway was a serious impediment to transit development in Toronto - because now we have this small piece of infrastructure built to such high standards that any crosstown route across the north of the city which doesn't implement it in some way seems a waste, but which is too poorly located and ineffective to actually accomplish anything.