There's a real risk in attempting to define exactly what "socially suboptimal" uses for land are. Everyone will have a different opinion on how they want land to be used.

Worse still, your definition means that any unused land is socially suboptimal and should be disincentivized through taxes. Given that land is finite, how do we guard against eventually using as much land as possible? And where do we get all the resources to develop and maintain the land as well as all the consumables used by everyone living there.