I am not sure how 1) can be addressed avoiding duplication with ECLRT while serving ACC and ultimately Meadowvale as proposed in the SSRA report. And 2) is given an out by the said SSRA report - their Wellington Scheme is pretty much a DRL (though it needs improvement in the core section). That aspect of the project should be started concurrently - use Union Station as a stop gap before shifting north to an underground alignment - or maybe even both.
Well presumably the ECLRT would be permanently truncated at Weston, and a GO RER branch would serve points west of there. I doubt there would be any kind of concurrency, given the relatively low ridership on that corridor. They may add a couple more local stops though, potentially mirroring the subway stop spacing on Bloor for that stretch.
And yes that's my point with the SSRA report's Wellington scheme. If you ditch the assumption that the DRL needs to be a TTC subway, then you open up a whole new realm of possibilities for integration with the RER network. It extends further into the suburbs than a TTC subway ever could (unless there's a blank cheque), it solves the capacity crunch at Union, and it provides the connectivity to the shoulder areas of downtown.
Your concurrency point I absolutely agree with as well. Route all GO RER services into Union as an interim measure until the tunnel is built, and then shift the Toronto-centric services (SmartTrack or whatever equivalent) into the tunnel. This would then allow for a boost to 905-centric services, which by then should have the local transit infrastructure in place to support a higher level of service.
Right now the biggest obstacle to increased service in the 905 is the lack of local transit infrastructure and services to bring people to the stations. GO usage is pretty much limited to parking availability, so bumping service up too much too soon without the local infrastructure to support it would be an operations black hole. But by the time the Central Tunnel (or whatever you want to call it) is ready, those local services in the 905 will have had time to mature, so replacing those slots at Union that were previously Toronto-centric trains with a service boost for 905-centric trains may actually work from an operations perspective.
I'm guessing the Relief Study will say something like "SmartTrack/GO RER will provide some relief, but DRL still needed in 15-20 years"
The TTC study may say that, but listening to what's coming out of the various Metrolinx reports, they're looking at the DRL as more of a component in a regional network than as an expansion to the TTC subway network. They seem to be looking at it as the solution to the capacity crunch at Union, with the side benefit of being the solution to the capacity crunch at Bloor-Yonge. The TTC by and large is just looking at Bloor-Yonge.
