I really don't understand this sudden surge/trend of musicians thinking they can successfully write and distribute a decent book, of any kind.
I totally agree with you, its a general trend with people wanting to say they're writers, or thinking they're writers, when they've actually never really written anything. Frank may be a great song writer, but a novel is a completely different process that I doubt many musicians would be able to successfully complete.
But more importantly, this is just an off-hand comment he made about how cool it would be if he just dropped a novel next year. There's no indication that he'd actually write one, just like there's no reason to believe he'd design a stadium. Not a serious statement at all.