Never going to happen in the USA. Not in your lifetime or mine.
Neither will a European style social democracy. Anyone who suggests to the middle class that their taxes are going to double to pay for it (which is what it would take: for one example, Canada’s top marginal rate on the rich is several percentage points lower than ours, but their effective rate on the middle class is double what ours is) has a short political lifespan.
I think the answer is not going to be “welfare” but a reverse tax paid for with a VAT.
Welfare is welfare, and we already have a reverse tax on the lower income bracket.
There are several interesting ideas kicking about on how to address future challenges in this regard. My personal favorites are cutting the official “work week” from 40 to 32 hours (forcing more jobs to open up) and a guaranteed job benefit, paid for with not a VAT (puts the brakes on economic growth) but a financial transactions tax.
Automation is going to eat up a lot more jobs before it’s done. And a libertarian paradise where everyone on the left end of the bell curve starves to death isn’t going to be acceptable.
No libertarian would ever support that idea. We believe in the concept of the civil society.