I don't think the unknown Flynn is the answer to Jet's problems. It feels good but he couldn't even start on his own team.
I don't think ANY GM is going to hamstring themselves in 2013 by making such a bold deal. 2013 is a rebuilding year - any way you cut it - and Rex may be gone in 2014. A GM is going to want to take a conservative approach and build through the draft.
So what - even if we stick with Sanchez - it's one more year that isn't going to be great anyhow. With a few better players the Jets are capable of going 6-10/9-7 with Sanchez - why bother hunting for some panacea when the rest of the team isn't ready for a big push? Far too much to fix atm - and far too little flexibility.