> One tweak they apply is that rent-control does not apply to new developments, so creating new flats is more lucrative than turning old buildings into luxury developments.
Typical YIMBY broken record here, but in the U.S. it's more or less illegal to build new housing on almost every inch of land (especially in the most expensive cities). We don't need to develop baroque incentives for developers to create housing; we need to stop making it illegal.
It's illegal to build at all on some plots of land. It's illegal to build apartments on most plots of land in most cities (this is called "single-family zoning" and it dominates most U.S. cities). It's illegal to build large apartment buildings on still more plots of land.
And then, yes, of course, there are some plots of land where it's legal to build one or more of the categories listed above.
The places where housing is scarce are in the former groups, by and large, not the latter, which is to say the problem where housing is scarce is indeed that it's illegal to build enough housing there. Those places don't need to incentivize development. They need to make it legal.
Typical YIMBY broken record here, but in the U.S. it's more or less illegal to build new housing on almost every inch of land (especially in the most expensive cities). We don't need to develop baroque incentives for developers to create housing; we need to stop making it illegal.