It's a fait accompli. The road to travel now is a Constitutional Amendment making it perfectly clear that the "full faith and credit clause" does not apply.
The Massachusetts legislature refused to act a couple of years ago when they were presented enough signatures to make DOMA a ballot issue. It's no secret why they failed to act. They are liberals and cultural progressives, the enemies of conservatives.
On what grounds? The Mass Supreme Court interprets and rules based on the Mass state constitution. SCOTUS has no jurisdiction to overturn this court.