There is now no language in the Constitution which blocks polygamy.
State laws (ex. Utah) on the subject of marriage ae now null and void.
Tradition (ex. no homosexual marriage) is gone - it's no longer a factor.
Religion (ex. no homosexual marriage) is gone - it's no longer a factor.
Question: Why is the world WOULDN'T polygamy be next? What blocks it?
Nothing now other than social non-acceptance and we see how quickly that evaporates. The folks lobbying for polygamy will use the same arguments homosexuals did.
Based on SCOTUS decision then nothing blocks polygamy as it can fall under the equal protection clause and the homosexuals need to shut up about trying to stop them seeing as their sham of a pretend marriage is as lawful as polygamy.