Almost all of the polling I've seen (and Ive seen a lot for obvious reasons) shows "M4All" tests great, until you tell people how it will work, at which point support drops a lot. M4All is great branding but not sure we can say people are fully behind the policy. Granted its a terribly complex idea and hard to convey in a simple exit poll.
My sense and professional judgment are people like a choice, ie public option, but dont want a true single payer system. Its interesting that people are now opting out of traditional Medicare and private medicare options funded by Medicare. I think this is the future of HC in the US as we see in both medicare, medicaid and the aca.