This is an interesting idea. I see this transformation of marriage into a semi-open relationship as just another step towards the obsolecence of marriage altogether. The institution of marriage originally (a long-ass time ago) came about as a tool for men to manage their property and their family, which were virtually the same thing. Now that we live in an age where property is personalized and people (supposedly) don't own other people, I would argue that the whole arrangement is really unnecessary. It is common knowledge that rates of divorce are higher than they were 50 years ago in countries like the US and UK, and furthermore that rates of marriage are declining. So as I said, after reading this article I am more convinced that people today are more and more willing to challenge or even ignore "traditional" (read: monogamous) marriage. In the next 50 years it will be fascinating to see how couples who choose to live together and not marry are perceived by mainstream society.