To be clear though, any such consensus _could_ theoretically be modeled using a smart contract between multiple parties, including how ownership was to be revoked (e.g. "party `X` owns thing `z` unless party `Y` says otherwise").

The challenges are in:

1. knowing ahead of time what the parameters and participants of the contract need to be ("I own the house I paid for... unless 'the government' invokes eminent domain")

2. finding the usecases where it's even beneficial to store proof of ownership in a distributed fashion (rather than at, for example, town hall).