I am the post's author, and I was referring to a specific building [1]. My understanding is that the owners bought it, unlisted, with the intent to develop it into something else. The City then suddenly made a case for designating it as a heritage property.

This is an area with powerful neighbours who have a lot of time on their hands.

I actually think there's a strong case for preserving this property. I love the look. The architecture is very unusual for Toronto and it looks striking. But, it is always a bummer when you purchase a property with plans to do X, and then get a surprise designation after you pay the money.

[1] https://www.toronto.ca/legdocs/mmis/2018/cc/bgrd/backgroundf...

I've read someone mentioning that in the UK such matters often resolve themselves by means of an accidental fire.

Not true. Many buildings are on the heritage “of interest” list and remain there for decades and as soon as someone goes in for permit to do something drastic, it gets moved to the heritage protection list and your rights are severely limited. Sometimes just being in a heritage district but not having a specific listing is enough to get classified when you want to do work.

This is from direct experience in Canada working in this industry.

Where I live, an administrator can decide that there is insufficient evidence that a property is not historic to permit unrestricted changes.