Blockchain offer no satisfactory solutions to this, houses can change, people can lose access to identification, people can be evicted, people can make mistakes. The last thing I would want is to be evicted with (by design) no chance to get my house back because my computer got hacked.

I cannot understand how at the same time lots of people are worried about "superintelligent machines eating the world" and proposing to remove humans from all important decisions in our lives.

Next step is to build a social graph on blockchain?

In the US there's only one real estate database per county, maintained by the county government. Owners can purchase title insurance to protect against other claims or liens, but the insurance company doesn't hold the title. And title insurance is quite cheap because in practice the risk is miniscule.