It will be some unelected federal judge who will approve polygamy using tortured legal reasoning and the SCOTUS will uphold it 5-4. Federal judges will also uphold persecution of Christian churches that do not support gay marriage
Yep. That's the route that homo marriage took. Started in 2003 in Massachusetts. Kennedy cited the numerous court decisions, substantial amount of public discussion, referendums, and so on. But the number of judicial decisions was a big factor in inventing or imagining a fundamental right to homo marriage.
The poly marriage argument may be different, involving acceptance by mohammedans as the wedge to justify lower court decisions. IOW, poly marriage may be the free exercise of religion, and who is the government to stand in the way (this decision would reverse the old Reynolds poly marriage case).
Anyway, the process of getting SCOTUS to jam poly marriage down the public's throat is to first get lower courts to do so. It'll take some time, 5, 10 years maybe.