This idea is intriguing and it probably has some merit. Unfortunately, when America has such a large segment of the population that is vehemently opposed to social programs, something like this would be a very hard sell here in The States. Though, I do have to admit while I haven't looked too deeply into the idea, the concept of a Universal Basic Income for some reason has similar connotations in my mind as the libertarian idea of a flat tax, something that sounds good on paper, but might not really work out all that well when implemented in reality and scaled up. A lot of programs, welfare, taxes, etc. are complex because there really isn't a one size fits all solution to every situation.
You're right - that's why I prefer a negative income tax. One big problem with UBI is you give out money to people who don't need it. Negative income tax doesn't have this problem. The USA doesn't have a true negative income tax, but there is an earned income tax credit that behaves the same way, but only for people with jobs. It was put in place under the Clinton administration and seems to have been a success at reducing poverty. Politically, it might be easiest to focus on expanding this program. A compromise might be struck with budget deficit hawks by cutting other welfare programs that are less effective.