Everybody is a potential interviewee. Everybody has most likely got some interesting information to tell about his or her life, although the older you are, the more you are likely to have to share.
The 'difficulty', for want of a better word, is knowing the questions to ask to get that information. I could, for example, ask anyone about their favourite book, band, film or tv programme. How much better would that type of question be if someone on the site knows you read 'Harry Potter', or 'War and Peace' twice a year because you've played all their quizzes on those topics and exchanged lots of notes with that person? It's why we ask the prospective interviewee to nominate who should ask the questions. I've given just one example - maybe you've abseiled down the Empire State Building or walked around the coast of Britain, or contributed to the sewing of an American quilt/copy of the Bayeux tapestry, been a backing singer for Madonna. Nobody's likely to ask about that if they don't know you've done it.
You don't need to be a prolific author. You could have built up a network of FT friends by playing quizzes, or contributing to chatboards or writing a blog as well as by writing.
The interviews take quite a bit of work - for me (currently), the people nominated to ask questions and the interviewee, having to think how best to answer. We want people to look at the interviews and think 'oh yes, I'd really like to know more about...'.
Editor - Animals & Sci/Tech