Its not actually inconceivable. The world is changing. We have to suppose a new sort of industrial infrastructure. One that doesn't need (so many) people to run it. The level of lifestyle (or standard of living) can certainly stay high, even increase, without so many people working. Its already happening!
Rising unemployment is partly due to a rise in automation and industrial efficiency. The ultimate limit is, (almost) nobody needs to work, yet goods are still available and continue to increase.
Even if you could provide that same level of basic income, there's an inherent unfairness between someone who worked in the private sector and saved $1MM for their defined contribution (401K-type) retirement and people who worked for less salary all that time and now rely on their defined benefit (pension) plan. Let's say both are living off $50K per year (4% plus a slight drawdown for the 401K person and $50K in straight pension for the other).
If you use basic income to replace the pension money, but don't confiscate the 401K savings, you've massively disadvantaged the pension holders. If BI is $25K/yr, now one person is living on $75K per year (or $65K/yr and passing along a $1MM inheritance) and the other is living on $50K and will die without a nest egg to pass along.
Trust me, those pensioners are one pretty well-organized voting bloc... ;)
Yupp, pensioners (especially in the US) are a big problem to plans like this.
Ideally (state) pensions would become obsolete and retirement funds would become an entirely personal issue (as they've largely become in Germany btw -- the tax-funded pensions will at best barely keep you above the poverty line even if you've worked every day since from 18 to 65).
So as far as pensions go you will have to go with an unfair transitional period. You could freeze the pensions and pay them out in proportion to the (now discontinued) contirbutions (which at least in Germany is how it works already) on top of the BI. But for pensioners you pretty much end up allowing them to "double dip" or drawing some arbitrary cut-off line for who will receive BI or only grant BI in proportion to the pensions.
But as you may have noticed I'm not well-versed when it comes to US pension systems. I'm assuming it's similar to ours but considering even healthcare was purely defined by the employment contracts until fairly recently I wouldn't be surprised if it's drastically different.
Rising unemployment is partly due to a rise in automation and industrial efficiency. The ultimate limit is, (almost) nobody needs to work, yet goods are still available and continue to increase.