I am willing to bet that there is currently more fill looking for a new home than has been expected of late. With all the pits being dug in Toronto at the moment, the construction industry must be exceeding what was expected of it.
The Ministry of the Environment has capped both the area that can be filled at the Leslie Street Spit, and for how many years they can continue to expand it. I would be interested to know close the amount of fill they have been receiving lately is to projections.
A serious hill out there like the one you mention Ed would be pretty interesting. As a lookout high above the rest of the portlands and islands, it would have pretty amazing views.