This is why almost every piece of legislate introduced into Congress opens with language stating is is implemented under the Interstate Commerce Clause, not the Supremacy Clause.
The ultimate Constitutionality is not does Congress have the authority to do something, but does that something constitute interstate commerce. Unfortunately, the SCOTUS has a history of deferring towards Congress.
The real Constitutionality test for ObamaCare will be if Congress has the right to demand an individual purchase something or otherwise have a tax levied.
There will likely be multiple 14th Amendment Equal Protection Clause challenges to ObamaCare.
It seems to me that Social Security and Medicare both fit this description...ergo...