Really, we are talking about the difference between High/Low platforms right now. The 427 part of the OL will reach Pearson from the south, so effectively paralleling the EW Pearson extension. Its not just the MCC section that will go south. Given that extension isn't under construction right now, I imagine they are working out how to future-proof it to serve as many kinds of trains as needed. Determining what this section will look like is a very small piece of the pie with a few options, anyway...
