Hey why not! If everyone consents and are in agreement, then go ahead. I don't personally feel it should be illegal now.
I say yes to polygamy only if women are allowed to marry multiple men. But I feel like a law like this would only be pushed so men can have multiple wives and if women married more than one man, they would be called hoes.
As long as folks are grown and willing, they should be able to partner with one another in what ever ways they want. Now, how they should file for taxes and partner benefits is another question.