A subway extension to Cooksville via Sherway and the Dundas corridor would probably attract a lot of ridership and directly links the Hurontario corridor's transit line to Toronto. It would also make for a good jump-off point for Dundas BRT heading west into Hamilton.
It will not to justify building the line in the first place.
One has to look at not only the current ridership, but projection numbers at least 30 years down the the road as well what is plan for the route.
Bulk of the current ridership on Dundas is between Toronto and Hurontario with riders using Dixie & Tomken to get to/from work as well Hurontario to/from Brampton. Riders going to Toronto in the end is less than 30% then staying in Mississauga.
There are no plans for adding density or development to Dundas at this time, with most going to Hurontario and the city core, as well over at Erin Mills & Eglinton. Only big box is getting built at Dixie with a Chinese style mall of 100 stores or more, east of Dixie that being trying to get off the ground over 5 years thats has been vacant for years.
As for going west, the real drop off point is Mavis Rd for the local with a low number going to 403. One reason the express bus was kill going to Oakville. Neither Oakville or Burlington have the ridership for good quality service let alone going to an express bus before moving up to an light BRT and then BRT, considering it been in their master plan for over 15 years with a true BRT to be built come 2020 on those plans. Not going to happen come 2020.
When people really look at everything and do some vision, subway in Mississauga will never happen for anyone a live today, sorry to say.
As much As I want to see LRT from Kipling to Hurontario now, ridership is not there to support it. If this was the US, the LRT would be built, since they build these thing under 5 or 10,000 riders a day. They wouldn't build a subway.