I believe that was one of the concessions they requested but analysis of the station showed it was an excessively poor idea in many ways, even worse than Kirby for instance from what I recall; namely the costs and negative impacts on ridership from upstream passengers exceeded the benefits of the miniscule projected ridership. I think it was also a little too close to the overpass which complicated matters substantially.
Even the other requested station at Bloor-Lansdowne has been found wanting for ridership, although it was approved in the end. IMO that one is necessary, a connection to Line 2 would be huge and open up GO for a lot of people who work on Bloor West and make it more enticing even for those heading to U of T or Bloor-Yonge. I think that is an example of where the reality is likely to exceed estimates and models. The 512 is not nearly such a major transit line, there aren't really any colossal major employment sites along St Clair, and Downsview Park/Caledonia+Line 5/Lansdowne will provide good access between the GO line and that neighbourhood.
