There are ways of making this work, and you can have carrots and sticks, for example:
- You can limit the requirement to certain zonings and types of buildings (multi-family and commercial buildings), or specifically make some exempt (SFH, Townhomes, etc).
- We know that a lot of these sites are demo'ed because of property taxes being lower for vacant land, for example. The city can use this fact to create a sort of "subsidy" to prevent demolition: if a developer submits a Demolition Permit without the accompanying Building Permit, the city lowers the taxes for X amount of years, so as to keep the building standing, and maybe even in use. During this timeframe, the developer has to submit their Building Permit and start building, and the Demolition Permit would only be approved when the Building Permit is submitted.
If they don't start building it within the timeframe,, they have to pay the tax delta, retroactively. This has the added benefit of potentially keeping some businesses open and in place for a bit (or a lot) longer, and even activate, albeit temporarily, some buildings that are destined for the chopping board.
I know this sounds simplistic, and there are probably many shortcomings, as well, but an idea like this could be a starting point to getting something going, in this sense.