TTC has struggled to keep the Queensway trackage level for decades. Lots of different maintenance methods, all of them leading to the same result - a bumpy, swaying ride with slow spots and operators not wanting to take chances by running at full speed. It seems there is no way to keep tracks sitting on loose-soil ballast tamped down properly.
I interpret this decision as the TTC throwing up their hands and admitting defeat.
I like the grass median idea, but only if it maintains fast safe and comfortable operation, and only if track maintenance costs remain reasonable. TTC doesn't appear to have this capability.
Honestly, I'd settle for an astro-turf like solution instead of just plain concrete. It doesn't need to be functional, it just needs to add some green in the middle of a roadway.