I mostly agree with the implementation, however I feel like offline events that require presence at the specific place at a specific time would be too cumbersome for many people, thus limiting the adoption of such approach. Plus, there's a trust aspect (how large the verifier party should be?) and lack of anonymity.

There's a project called Idena which does synchronous verification events online, where people should solve a Turing test in a strictly limited time. It's not perfect, but it does create a trustless network of semi-unique pseudonymous identities