A global personhood system based on Bryan Ford's Pseudonym Parties.
Pseudonym parties, either offline or online, needs to process a global population in a short period of time, hundreds of millions of transactions per second. A blockchain cannot scale to that, but post-blockchain systems like BitLattice could.
Online Pseudonym Parties is not a UBI system, tough it does have tokens, or equivalents of tokens, which can have value.
Online pseudonym parties involves every single human being in government positions, pairs verifying one another 1-on-1 in a global, monthly, pseudonym event.
Johan
The network can be attacked through collusion, that is the only significant attack vector. For example, 10% of the population who colludes against their network, can provide bots with 0.5% of all personhood tokens. Mass-scale collusion tends to be a problem in many systems, including representative democracy and proof-of-work which can both be 51% attacked.