It may well, of course, just fade away. I found some stats:
http://www.guardian.co.uk/news/datablog/2010/feb/11/marriage-rates-uk-data

and it looks like the rates of marriage have more than halved in the last 25 years.

With children born out of wedlock up to nearly half, I suspect we're going to hit some kind of tipping point in the next generation:
http://www.telegraph.co.uk/culture/tvandradio/9090627/BBC-asks-children-to-organise-their-parents-weddings.html

The question is, what replaces it, if anything? Are people not getting married because they can't see the advantages? And if so, is there something legal that should be made easily available with clear plus points?