If the Supreme Court does declare this, they will by default also be declaring that polygamous marriage is a constitutionally protected right based on the very same legal grounds.
Indeed. Right after the Court ruled in Lawrence vs. Texas, a polygamous trio (husband and wife looking to add on another wife) attempted to obtain a marriage license and are now suing Salt Lake County, citing that L v. T's reasoning concerning consenting adults and state interest clears the way for polygamous marriage. Frankly, I agree with them. If the SCOTUS is the final arbiter of moral issues that they are setting themselves up as, L v. T legalizes any marital or sexual arrangement consenting adults desire, end of story.