My big problem with the City's 'skyline tapering' policy is that, when combined with the City's NPS shadowing policy, it virtually guarantees that downtown Toronto will never see an 'official' supertall.
The NPS shadowing policy means that nothing taller than FCP will ever be built in the MINT area (in fact, I understand that FCP itself would not be approved if it were proposed today). The one exception would be the new portion of downtown being built south of the tracks, but we are running out of available plots in the area zoned for unlimited height, and it's unknown (to me) whether any supertalls will be proposed in one of the few remaining undeveloped, unlimited-height, plots.
The skyline tapering policy means that nothing taller than the tallest downtown buildings will ever be built in the surrounding areas either, meaning no supertalls there as well.
It is certainly possible that a 300+ metre building might be built well away from downtown (1BE and Aura show that very tall buildings can be approved in their respective areas). I think that Toronto's best chance for an official supertall might be in the Yorkville (or possibly Yonge/Eglinton) area, not downtown.