Yes, they strip malls could be redeveloped. Anything could happen. But, its not likely going to happen, (if its going to happen), in a reasonable time line. Plus, if all that you needed was density to justify a subway line, you could definately build the DRL line right away.
The longterm plan for a major road in mississauga like Dundas is LRT. So, if you build the subway line to hwy10/dundas, and then turn right ('L') up to square 1, what are you going to do with dundas west? Unles you build for the far future, and build an expensive little transport hub in the strip mall at that intersection, to allow for future connections to the hwy 10 LRT and a future dundas west rapid transit line, it doesnt make any sense either way.