Good for Mexico. I'm in favor of a different solution, however. I would like to see my government get out of the marriage business altogether. Any group of two or more can get a civil union, as long as they're consenting, unrelated adults (I think incest should be illegal due to the effect on progeny). If those people wish to get married, they can find a church that is willing to do it. Churches should be free to discriminate against whomever they wish. If they don't wish to marry a gay couple, a group of polygamists or even an interracial couple, they should be free to decline them. Individual groups can discriminate; our government can't.
I really like this solution. There is no need to call it marriage, goverment should deal with civil union only.