From everything I've heard and read, there doesn't seem to be any legal wall to block polygamy at this point. I don't really care from the "minding my own business" standpoint and believing marriage should have nothing to do with government.
The problem with polygamy would be if, like with same sex marriage, the state forces employers to cover spouses on health care etc. In this case, spouses really is plural. That could cost business a lot of money.
The other legal battle that will likely ensue will be forcing churches to perform gay, poly, etc. marriages with the stick for not doing so being revocation of tax exempt status.
Equality =/= freedom.