Full benefits could phase in over time. You could get increasing discounts on public services until you reach full state membership. This would be no different than out of state school fees.
Durational-residence requirements still exists. E.g., paying in state vs. out of state tuition at a state university, which commonly requires a year of residency. [0, 1] State-provided healthcare could be provided in a similar fashion through state-administrated health insurance that has different rates for in state and out of state. There could be a durational-residence requirements for in state pricing.
"If the purpose of the requirements was to inhibit migration by needy persons into the state or to bar the entry of those who came from low-paying states to higher-paying ones in order to collect greater benefits, the Court said, the purpose was impermissible"
It's obviously hard to know for certain what SCOTUS will do, but under that standard it sounds like having health care benefits only available to long term residents would be on very shaky legal ground.
The trivial solution is to tie residency to property ownership or property lease, and payment of property tax. Then use the prop tax to pay for the health care, because almost all health care is local anyway. Have the hospital or clinic or whatever bill the municipal taxing authority wherever you live; for most people the house you live in.
Determining residency is not rocket surgery; could steal the entire system from state income tax codes.
Just another example of the failures of the Constitution in the modern era. The Federal government is the only one that can reasonably do Universal Healthcare, or any kind of economic stimulus in crisis, but it fails. States are powerless to try to fix it on their own.
