If you install an AEV suspension on a 2012 JKU, you will void the warranty for only the oem suspension. Add larger tires nd appropriate wheels and then there is some confusion here and there. For example, a dealer might argue that a ball joint issue was caused by the larger tires, or wheels with less backspacing. Dealers are different, some are into modified Jeeps, or even modify them prior to or after sale, some are not....
As for installing an AEV kit, generally you can improve anything with aftermarket parts. Yes the AEV kit is a well designed suspension system, but from the sounds of the OPs intentions he will be leaving the vehicle stock for a good while. A lot of people have a hard time voiding there warranty and spending the cash right after they have bought a 30k+ car.
The same can be said for the FJ... all you have to do is spend money to make it more off road capable.
But, in any event, the whole of the warranty isn't voided. Also, the burden of proof resides with the dealer, and not the owner, though fighting the issue might lead to a phyric victory. Having a brain cramp at the momment and can't recall the name of the act, but it is federal law of the land. That law applies to Jeeps and also to Toyotas... But, no matter how much you change on the Toyota you can't make it as capable as the Jeep.
I have a 2010, but it has a Hemi and the 545rfe, AEV 4.5" suspension, 37" BFG A/T's etc, etc, etc. Rides better than my wife's Range Rover Sport, or my Suburban, or my wife's all but stock JKU. Handles better than the Suburban or stock Jeep, damn near as well as the Range Rover, which has the oem Perrelli street tires. Other than three Jaguars that I have owned over the years, it is by far the most satisfying vehicle I have owned.
My wife's Rubicon Unlimited is a 2008, and but for a TF 2.5" BB and a set of Spider Trax wheel spacers it is stock, and still riding on the oem BFG M/T's. Its been trouble free, but it is going to be sold for a new 2012 Rubicon Unlimited.:wings:
BTW, anyone interested in a cherry 2008 Rubicon Unlimited with 18k miles? Rescue green, auto, soft top and half doors. The upgraded stereo. :sombrero: