Depends if they can get the developers of Sherway/Cloverdale Mall to stump up some cash.
Combined with a very modest extension of the line to serve the (long proposed) Obico Western Subway Yard - I could see this happening, esp. if built as elevated.
No need for super large bus terminal either - given the new regional one at Kipling.
I personally would prefer an extension just to Cloverdale - shorter distance and easier to build (no need to cross Highway 427).
An extension to Cloverdale has an excellent case.
That said, the Sherway Garden site as-is, is a very large employer; redevelopment here will make it a major population node as well; there's also a hospital across the street (more or less), which is set to get considerably larger in the years ahead.
So the case for Sherway is not without merit.
I think I would argue here for a continuous build extension to Sherway.
ie. build to Cloverdale, open Cloverdale then just keep going. This is a way to lower the incremental cost of construction and pick up additional riders long before the entire extension is complete.
In terms of compelling business case vs other extensions/investments; I would argue it clearly ranks behind extending Line 5 (Egilinton) into Pearson, but after that......its case relative to other subway projects in the pipeline isn't uncompetitive.
I would, however, rank it below upgrading Milton GO to 2-way, all-day, 30M or better service.