I don't have any stats, but I know that very few of those who submit are selected. My wife and I received a long form write-up (just under 700 words). The process started with our submission on the website, but then we got a call from a writer a few weeks later. Between talking to us, our parents, and our minister, I'd say he put at least 10 hours into researching and writing.

A day or two before the wedding, he told us that he wrote both a long form piece and a shorter, more typical piece. He wasn't sure which would get published, but he was obviously pushing for the longer piece to get in. It did.

Oddly enough, our write-up isn't included in the Rap Genius dataset. Maybe it's too recent or the longer write-ups aren't included.