Erieblogging: Day Eight

I’m posting an un- or underexplored question about Erie Railroad Co. v. Tompkins  every day this month (parallel posted on my own CivPro Blog).

 Today's question: Assume that the Pennsylvania Supreme Court has held that Pennsylvania’s prohibition on interspousal negligence actions does not apply to a suit by a New York wife against her husband concerning an accident in Pennsylvania. New York law, it concludes, should be used instead. A federal court in New York is entertaining the same type of case (that is, a negligence action by a New York wife against her husband concerning an accident in Pennsylvania*). Does Erie require the federal court to respect the Pennsylvania Supreme Court decision concerning the scope of Pennsylvania law? Is it forbidden from applying Pennsylvania law? 

Kim Roosevelt has argued that the federal court is bound by the Pennsylvania Supreme Court's decision. I think that whether it is bound is a question of state law that can be answered only by certification to the Pennsylvania Supreme Court. My guess, however, is that if the matter were certified, the Pennsylvania Supreme Court would let federal courts come to their own conclusion on the choice-of-law issue. In other words, it would choose Swift over Erie. 

*Assume it gets subject matter jurisdiction over this cause of action through supplemental jurisdiction.