Yes I know. And I'm telling you that it's a bad idea. It was a good idea ten years ago, but now that construction has begun on AD2W infra between KW and Guelph, it makes more sense to just wait until construction is complete and we can introduce regular, dependable service.
That shuttle would not be a dependable service. It couldn't run while CN, Via or peak GO trains are using singular existing track, or when the line is shut down for construction. It really doesn't seem worthwhile to increase the cost of construction, use chronically scarce crews and delay the introduction of regular hourly service from KW to Toronto just for a few intermittent shuttle trips between Kitchener and Guelph.
It has nothing to do with the Brampton bottleneck. The construction for AD2W is in Kitchener, Breslau, Guelph, Acton and Georgetown. The expansion east of Georgetown will occur while hourly service is already running to Kitchener.
There is certainly a lot of demand between Kitchener and Guelph, but how much of it can easily get to and from the current Kitchener station? It has poor transit connections, poor walking and cycling access and not very much parking. The new Central Station will have orders of magnitude better connectivity, and would thereby capture more of the demand. And guess what: as soon as that station opens, there will be regular hourly service to Guelph.