This is no different than contributing to the "right" Congressional candidates with few dollars so they control hundreds of billions of dollars of policy (or in this case, trillions of dollars). This isn't anything new or weird. NGOs face this issue all the time, having to prove out models before they'll get gov or foundation funding.
I'm not here to convince you, and if you're not a policymaker or the Fed, I don't have to.
https://news.ycombinator.com/item?id=23258277 (HN: Indian farmers to get direct cash benefits)
https://news.ycombinator.com/item?id=23351708 (HN: Spain approves national minimum income scheme)
I'm a UBI opponent, a short term HM proponent, but I think my posterior probabilities would shift depending on the size of the effect and the duration over which the experiment was performed.
Medicare Part C, or Medicare Advantage, is much closer to a UBI than "Original Medicare". Nearly 40% of Medicare beneficiaries are enrolled in a Medicare Advantage plan.
Cash alone makes a poor safety net, because humans are humans.
The common theme is that there is some degree of government intervention and regulation, but having the government be the sole payer is definitely an approach, but it's by no means the only approach, nor even the best approach.
Social Security and Medicare are already UBI at large scale, but age tested (62 is the minimum age, 70 the max for social security benefits, age 65 qualified you for Medicare, US universal healthcare for seniors). Caveat: you needed to have worked and earned certain amounts to qualify for Medicare and your benefits level.
To test at small scale, you'd need an endowment that would use the investment returns to pay folks their UBI, and then payroll taxes that would include OSDI so they'd gracefully land onto Social Security and Medicare when they reach the age that qualified them. Pick small cohorts: students in their early 20s, some middle age folks mid career, and folks near the end of their career in dead end industries (ie coal). Observe and report.
If you can "cross the chasm" (see: companies going remote first after being forced to see if it can be done with COVID), it then becomes PR getting an audience with the Fed and Congress to rejigger monetary and fiscal policy to print and distribute accordingly. Can't see we can't print, money printer is running exceedingly fast right now [1], but can we put that money in the pockets of average citizens instead of simply inflating asset values of the richest Americans? That's the question.
[1] https://fred.stlouisfed.org/series/WALCL