Any of the states that aren't party to it could file suit, and the ones that are against it probably would. There's also the bald reality that the NPVIC does overall advantage one party and disadvantage the other, and that "other" party is known to have much more of an influence in the Supreme Court.
They also won the electoral college. You have to ask yourself which party has a higher likelihood of winning the popular vote while losing the electoral college.
