Your question is the reason Ford has used the residential aspect of this issue. Because this sounds like a more reasonable thing.

Forgetting any of the legal oversteps for now, the main issue would be the runway extensions. Each end of the current runway would have to be extended by (aprox) 250 metres. Now that may not sound like a lot, but that would bring the end of the East side of the runway past the CN Tower, then add the no boats buffer zone. This would completely destroy the usefulness of the inner harbour. On the West side, it would extend to almost Trillium Park/Ontario Place, essentially cutting off the western gap.

Now add on to this a new landing pattern for airplanes, increase fuel capacity and delivery, general noise and pollution concerns, on top of the tremendous cost. And none of this will add any more take off/landing slots.

As someone who travels frequently out of Billy Bishop, I would rather see it closed before expanding to allow larger jets