How much would taxes have to increase in order to provide a UBI that would keep everyone above the poverty threshold? Have you actually done the math on this?
I don't think straight-up UBI would work, in the current systems. I think it would just make every affected good that much more expensive. A similar thing happened recently in Hungary with housing prices, when the government basically put subsidy into people's pockets. And the market just ate the subsidy.
I really do like the idea of a country keeping all of its citizens above the poverty line though. If UBI isn't the way, then some other way - maybe providing goods and meals instead of money? Taking a page from the Sikh's book.