So, five years of great QB play vs. the chance of a draft pick that many people doubt coming in and lighting the world on fire as a rookie?
Think of it this way--would you trade Luck or Newton for Rivers? No. Would you dangle RGIII, Manuel, Gabbert, Bortles, Locker, Ponder, Bradford, or Tannehill for his five years of high level play? These are all guys taken in the first half of the first round in the past five years by teams who are desperately trying to solve their QB problem.
If I'm the Titans and I have the shot, I jump at it. I keep Mettenberger and coach the poo out of him, and ride Rivers for as long as he will last. It's about the only thing I have to gain a little job security.