All of which reach beyond the blockchain. No-one is going to care that a 'smart contract' says that Alice owns a plot of land when Bob holds the real-world deeds.

The real world and the blockchain can only be linked when, as you say, 'the powers that be' decide to recognise the data. But then you've lost all of the advantages that the blockchain was claimed to possess. For example, if we need an entity to recognise that the land registry smart contract is valid, there's no more decentralization, and we might as well let that entity store the land registry in their own simple database. The blockchain becomes pointless and wasteful.