Uh, you got any kind of a source for that?
If you have being following things from the Metronauts days, you would see and understand that the Lakeshore line was looked at being 2 lines. There is talks within Metrolinx, even at BOD meetings, that the line will be 2 lines.
With GO maintaining ridership numbers for east and west, they see it as 2 different lines to the point you have more peak service in the west than the east since there more rider there now.
Since Metrolinx owns the tracks to the west now, GO will be able to run more westbound trains once there is enough crews to do so.
You will still see some runs like today, but not close to what we will see down the road in the way of service all day since the 2 sides will have different headways.
What you need to understand in looking at the big picture is land use, as that plays a big part for ridership. Since the east in heme in by the Greenbelt, there not much room for more development. At the same time, they like low density development. Even with the expansion to the east, ridership increase will be low to other lines, but mostly to the west line.
When you look to the west under the current system, there is a huge amount of land for development and with more density development taking place. Once the expansion takes place west of Aldershot, ridership will increase more.
The ranking of the lines is my view based on what can happen once all the lines are 2+ track for GO only as well the development that can take place along the lines. That is why I said Time will tell.
My great fear with GO leap frogging the Greenbelt, it will help to create the urban sprawl we have now in the current area, where these new areas will see and have the same problem that we have now considering they have no plans in place to deal with it now.
Going back to splitting the line, it will have to happen once the east section is electrify first before the west, since this will have the 2nd yard that will be electrify from day one.
Milton is a given as being #2 when it gets it 2 tracks and all day service since it needs more service now just for peak.
The Kitchener line with its expansion beyond Georgetown, opens up a new area for new ridership and development. As to how much is a guessing game at this time, but it can out perform Lakeshore East.