The type of motive power has little influence on train handling. Regardless of the power source, if anything greater acceleration = increased passenger discomfort beyond a certain range.
Logically EMUs are meant for more frequent runs with less capacity but there would need to be more EMUs and more drivers purchased to match the capacity of a less frequent diesel locomotive pulling 12 cars so it would be difficult for it to be cheaper. The EMUs would be providing better more frequent service but where are the savings going to come from?
Add to this the costs of construction a newer and improved way side singled system or implementing cab signaling. The Lakeshore corridor was built for mixed use application, it is not optimal for a high frequency passenger train operation (15 minute or less internals) because of the distances between signals (this also apllies to all other rail corridors in GO's current and future system). It will be difficult to provide an efficient and timely system without either improvements in signaling or significantly increasing the number of main tracks needed. A combination in both likely will be necessary though improved signaling will reduce the need for additional main tracks. In any case increased train frequencies due to the implementation of EMU’s will have this added cost.
breaking - their motors are probably 20x louder than an electric train
Accelerating yes, braking no. The braking of trains does not contribute much to engine noise. Power is drawn off the main engine itself to run a compressor which replenishes the main reservoir which provides air for the brakes. Depending on how much ’air’ was used to brake the train the engine may rev 20% higher or not rev any higher at all. In any case this will usually occur when the train is idling at a station and is hardly noticeable beyond a few hundred feet, certainly its nothing compared to the acceleration phase which I must admit is extremely loud. (Think about how I feel sitting inside one of these beasts!)
Canada already has one of the best rail signalling systems in the world, and with track improvements and grade separations that would come with electrification, I don't see why standards have to be as strict.
The track improvements are extensive and more are on the way. However the signaled system is flawed as I’ve mentioned above. Some of GO’s current and several future purposed lines aren’t even signaled or use an older tpe of signalled system.
Has anyone considered making a new commuter system from the ground up? I guess there was GO-ALRT, but anything more recent? There just seems to be a lot of problems with GO sharing tracks with freight trains, and indeed not even owning the majority of its trackage. Sometimes I think it would just be easier to start from scratch and build a totally separate ROW, probably near the existing rail ROWs but maybe not.
It would definitely not be easier to start from scratch and it would be prohibitively expensive. New ROW’s would involve extensive property acquisition most likely through expropriation. It would not be popular and would - to put it mildly, probably bankrupt the province.
So no it is not feasible.
GO owns several corridors already:
http://www.urbantoronto.ca/showpost.php?p=279079&postcount=104
On these corridors they control the dispatching of trains and the minimal freight operations that run on GO owned lines are not an impediment.