If Congress could decide to agree on something, they announce taxes are being raised by X% to provide Medicare for all next year. Next year, employers stop providing healthcare via insurance companies and everyone signs up for medicare. Done.
One of the huge fights about ACA from the left was so-called "Cadillac Plans": Unions negotiated excellent medical insurance coverage in lieu of wages for their members. If you suddenly axed employer-provided coverage, nearly every union in the US would want to renegotiate contracts to account for that.
