This is a response to various postings in other threads about GO equipment and will post my comment here for it where it should be
No matter where we were on our trip this summer, saw a mixture of various type of equipment from DMU to HS.
In Brussels, saw coaches added to double deck train with electric power pulling it. Most places have DD with a cab car at one end and electric power or diesel doing the push/pull thing like GO. Some trains were 3-4 cars long that either rain as a set or up to 5 sets
Netherlands run Sprinter trains as 4 car sets from Stadler/CAF that run as a single set or double, but mostly double. Did a see a 6 car train. Intercity trains ran as a 4 car set either single level or DD to 9 single level cars with electric power at each end. There are DD trains of the same length as well.
Both Belgium and Denmark have ICM DMU and EMU that can be spilt into 2 or more trains depending on their requirement. Found out on our trip on an DMU ICM that it became 3 sets and saw it break apart on the fly.
All the HS speed trains ran as a 2 set that were 7-11 cars long on trains from 15-22 cars long. All systems ran various types of DD trains as well EMU trains
End of the day, there is nothing stopping GO from having a mixture of equipment until the system is electrify or as plan. Even after the system is electrify, still can run a mixture of trains until existing rolling stock is replace as needed. Ridership will dictate the type of equipment for each line as well the quality of service. Trains using CN/CP line will be diesel/electric or another combination until such time both RR allow an overhead system in their corridor