I disagree that Pape should be the connection point for the BD since it is cheaper to build to Coxwell from Don Mills Rd.
I still see this DRL as an S-Bahn using double deck trains like this found in Vienna. Its a Stadler KISS 6 unit built in 2011. It can be someone else model.
Note: It can come in various lengthen.
I think the concept of building the DRL as a S-Bahn style service with double deck overhead powered EMUs is a good idea for many reasons, but is unlikely to happen due to an even larger list of reasons.
S-Bahn style services are used around the world, usually as a second network laid over an existing subway, as a hybrid commuter rail/subway system. Having ridden the Paris RER lines, most of my experience comes from them.
Building the DRL as an S-Bahn would allow for many routing options on the main rail lines, especially in the western end of the line outside the core. Based on the idea of the DRL ending at Bloor, an S-Bahn could continue outwards fulfilling some of the promises of frequent all day GO service, and on the lines that are scheduled to be electrified first. The line could also run to the airport, similar to the Paris RER. Assuming the UPX continues to run, this would add a second tier of service to the airport, with more stops along the rail corridor and then into the downtown, silencing many of the criticisms of the current UPX scheme. The large trains would have capacity for years to come, and would relieve existing GO lines and Union Station. Compared to a subway, it would provide equivalent service along the proposed route, with branches out to the Milton, Kitchener and Airport as far as is needed. Eventually, when the GO system is fully electrified, it would provide another option for commuters, and Bloor would be a major hub.
The problems start with who's going to build it. The TTC wouldn't want to have to build a completely new type of system, complete with another set of trains, that would appear to be serving areas outside of the city. Metrolinx has the DRL in their Big Move plans, but it's another new direction for them as well, and might not mesh well with their existing system initially. GO seems reluctant to run anything other then locomotive hauled trains. It would also be more expensive to start, but I think latent demand would quickly make it worthwhile.
Overall, brilliant idea, but... government.