I believe that they are planning on connecting to the east end of the subway platforms, not to the mezzanine at the west end. Digging a new connection that long would incur significantly higher costs, likely tripling the price. An eastern connection to the subway platforms accomplishes creating the second exit for Dundas West station, which every station, slowly, is getting for safety purposes, even if it isn't convenient for those transferring from the UPX or GO to streetcars and buses. I assume the majority of transfers would be heading to the subway line though, anyway.Designs are supposedly to be finalized by the end of this year and construction to begin sometime next year. But we've heard it all before..
Ideally, there should be a direct underground pedestrian tunnel connection between the GO-UPX station mezzanine and the mezzanine level in Dundas West subway station. Not sure how this would be accomplished without digging up Dundas Street West and Edna Ave (right after they finished replacing the streetcar tracks). The McDonald's would presumably be in the way and need to be removed.
But if they are only planning to take over part of the Crossways parking garage, with automated Presto gates, for only the east end of subway platforms, with a separated mezzanine, then passengers wanting to transfer onto a bus or streetcar would have to walk the entire subway platform length to the other end, and up to the mezzanine which of course would be absolutely ridiculous.
Yet, still, this is what I believe will be constructed. But fingers crossed until we see the preliminary designs.