The pick of Quinton Coples last night raised the question in the title since the Jets indicated they intend to play Coples on the defensive line. He is best suited as a guy to stick his hand on the ground and get up the field as a 4-3 end. The selection of Demario Davis might further suggest to some there is a shift in place. His 235 pound frame and sideline to sideline speed suggest he is more of a fit as a 4-3 linebacker than a 3-4 one.
I think this whole discussion is a bit redundant. The Jets have always been a multiple defense. They have tended to show more 3-4, but they have run plenty of four man fronts. They might play relatively more 4-3 fronts, but any shift will be nowhere near as pronounced as people make it out to be.
Coples and Davis have key traits the Jets love on defense, versatility. Coples will likely play mostly at defensive end, but he can move all over the place. He can play end in a 3-4. He can slide inside to tackle. He can rush standing up.
Similarly, although Davis' frame might be a bit small for a 3-4, his game can fit inside. He has a nose for the ball and is just as importantly strong. His impressive bench pressing at the Combine indicates he will be able to fight in traffic. The big shift on defense might not be schematic. It might be that the Jets are simply getting younger and more athletic.