The only way it almost works now is you pay into medicare your entire life just so you can have it from age 65 on. Sort of like a savings account but it only is able to pay for those today on medicare and not your own. A legalized ponzi scheme.
"Medicare for All" makes about as much sense as "Social Security for All."
The only logical alternative is phased in privatization for both. Something like 60 or older, not affected 100% of benefits, then dial down 3% per year. 59 years gets 97%, 58 gets 94% and so forth down to age 25 gets total privatization.
And stop paying benefits to those who haven't paid in a dime . . . that's what welfare and Medicade are for.