I think the only way it would make sense to trade Lynch is if we traded for or picked up a free agent that was a clear #1.  Then you make Trevor a long-term #2 and Lynch is expendable.  

But as much as I like Trevor, I don't think you can just say "he's our clear #1 for multiple years".  As such, WE'RE one of those teams you speak of that needs a good QB prospect for next year.  So it makes more sense to just try to keep developing Lynch for hope he has a breakout in year #3.  Many experts felt he needed at least 2 years of preparation anyway (maybe even 3).