Since I am renovating in the existing stock, I am not that deeply involved. But the mentioned plots are privately owned and a building obligation is notarized with the resale.
Maybe you would like to name the affected municipality, then one could inquire at their legal office how they handle this. As a "best practice" for other municipalities.
Two years ago, there was a case where a homeowner found out that the free plot below him, which had been free for over 30 years, was about to be sold and he wanted to buy it himself immediately so that no one could build there. Then the building obligation came up again and that he would then have to build.
Because of exactly such selfish idiots with the attitude "my greatest happiness is that others have none," the topic of building obligations keeps coming up. This is a burden for the municipal community. Living space always starts with building land, and others need some too.
In the 80s, everyone who contributed land to the development area also received plot(s) for it.
Land readjustments still work like that today. Every contributor in such a procedure may leave his regained plot fallow until doomsday – that cannot be prevented.
My hint was only to prevent that there might be special circumstances affecting the options available for the thread creator’s plot. Here, at least it is supposed to be prevented that the plots change owners and still remain undeveloped for decades.
I found (and still find) your hint valuable. My inquiry is only motivated by the wish to recommend the "trick" to other municipalities as well, since a building obligation (should be avoidable in places with reasonable people, though) serves the common good.