I dont think privacy will be possible at all with social media and artificial intelligence. bio-metrics can be digitally replicated without having to do clone a person. Simply tamper with a scanner and input someone elses code.
If we cannot solve the problem of preventing people from making multiple accounts then we will be moving toward a state run fiat UBI which will mean ultra tight borders and insanely limited immigration.
But if we can solve this problem, global UBI can be done right now. In fact multiple entities can offer different UBI services at the same time with different rules and advantages.
I agree, the current biometrics technologies make this quite difficult, but I wonder if we may have some workable solution in the future. Something beyond just an input device, but something more connected to the core of who we are that can't be replicated. If you like thinking about this stuff, you may enjoy Daniel Suarez's latest novel Change Agent. I love all his stuff and enjoyed this one as well.
One method of proving identity we already see right now is following and subscribing. Building a following is essentially identical to distributed identity confirmation. Youtube used a similar method for doing this with its ad sense system. It then rewarded people for building larger and larger followings.
Ultimately, a UBI cannot function in such a meritocratic sense because it would be antithetical of what a UBI is supposed to be. But it may seriously by the only realistic solution.
We are going to have to blend social media into the system somehow as a means for people to confirm identities. A UBI will likely be a capitalistic endever in spite of its marxist roots.
I mentioned a couple examples of identity online in the post I linked to above. Trust networks will be hugely important.