I think you mean "4.0L I-6", but at any rate, your relative should think long and hard before trading up. The TJ is aging, yes, but in some ways it's the last vehicle true to the tradition of the name Jeep made, and a Rubicon is the top of the line. The new JK's look really sweet - I'd buy one if I could afford one - but they're a completely different animal. The 3.6 V6 is a powerhouse that, after some teething problems got worked out, isn't a bad engine, but any future repairs to it will be much more complex than to the inline six. The 3.8 in the '07-'11 (or '12?) Wranglers isn't a bad engine, just barely powerful enough for the Jeep's weight and aerodynamics - an automatic with the wrong axle ratios is a real dog, while a stick shift with the right ratios is bearable. I'm not head over heels about the few 4.0's I've driven, speaking to their power output and NVH (noise, vibration, and harshness), but I still hold it's the best engine they ever put in a Jeep. The Pentastar might be the smoothest with much better power, but the 4.0 just has traits that match the Jeep idea: durable, torquey, and simple.