25m only applies to "towers" lower podium levels only require the code based 11m. The city generally prefers 15m, but will accept 11m.
Based on my reading, the 25m rule applies to the first 24m in height of a building. Assuming each floor in this building is 11 feet (10 foot ceilings + 1 foot floor) that would mean the first seven floors can have a smaller setback, but then it must be have a 25m setback.
So, if a developer wanted to build taller, the only solution would be if they built a 7 story podium and then any additional height would have to rise from the northern side of that podium.
All this being said, I doubt a developer should, would, or could build taller here. The density is set. As pointed out, they'd need to go through another site plan approval process, and I have a feeling this lot is already zoned to its maximum density. Plus, why would we want a taller building here? It's south of Queens Quay, the buildings should be short. That's been the rule for George Brown (1 and Arbour), Waterfront Innovation Centre, Corus, and the whole Tridel Bayfront development - the only exception to that rule so far has been this Pier 27 Tower and I have a feeling that was only because it was approved long before the others.
Could the sale be connected to Cityzen's longstanding problems at L Tower, which likely are quite costly to the company?
Could be. Logic would dictate they would only sell if (A) they need cash in the short-term, (B) they cannot develop the land themselves, or (C) they think there's going to be a market crash before they can build it. (B) doesn't make a lot of sense (though perhaps Cityzen feels they just have too many developments. (C) is a wild guess on our part, but doesn't seem likely. So (A) is most likely. Whether they need that cash for obligations in regards to L-Tower or something else would just be a guess though.