I think those are actual permanent government pensions. You’re going to have a hard time convincing people who get 5–10 grand a month to trade them in for 1 grand a month.
UBI, at least as a concept, does not replace pensions. What it replaces is social welfare spending, so stuff like TANF, SNAP, and housing assistance.
A LOT of those *types* of programs are state funded and administered. So, part of what the UBI fetishists seem to be assuming is that the states will agree to turn over their welfare budgets to the feds to create a big bucket of money to pay the UBI out of.
One can imagine the response that sort of proposal would get in Texas.
(It’s still not enough money) :-)