It's not as far fetched as it may seem. An overnight implementation is a heavy lift to sell to Democratic voters - BUT, an expansion of Medicare to lower the qualifying age by 10 years would expand the size of it to accommodate more people. That's very sellable to the voting population. And then after that, we can expand it by another 10 years. Then another. Then eventually, universalizing it would hardly be a step at all.
That would take much much longer than we want it to, but if we want it, it can be done. We just have to elect people who are at least interested.
Like I say, I could easily talk about this for a lot longer than I really have time for right now.