It's already happening in most everywhere that has passed gay marriage legalization. The ink was barely dry on the UK legalization before a wealthy gay couple decided to sue the Church of England to force them to perform a gay marriage, despite the law being passed specifically stating they wouldn't be compelled to.
http://www.huffingtonpost.com/2013/08/07/gay-couple-sue-church-of-england_n_3714609.html
Same thing happened in Canada.
It will happen in the US, without a doubt. They may not win but it will happen. Because to many on the left wing, gay rights is not what they're actually after. They want to go far and beyond that, and now that gay marriage is settled and legal, they won't just throw up their arms and stop.