As I suggested in your first post, get your Leaf up in the air and look at the suspension.
In the front, the wheel hub connects to the lower control arm and the strut. The lower control arm connects to the front subframe and the strut attaches to the chassis in the strut tower.
If you imagine making the strut 6 inches longer, you will push the wheel hub down (= lift the vehicle) but because the lower control arm has a fixed length and the movements of the wheel hub are constrained by the lower control arm, the hub will most likely not be perpendicular to the ground anymore. As you keep pushing the wheel hub down (lifting the vehicle) the wheel hub will move further and further under the vehicle on the path constrained by the allowable movement of the lower control arm. This will obviously affect handling and steering. At some point in your lifting adventures you will most likely start binding up your CV joints, which will get expensive and frustrating pretty quickly.
In the rear, you have a trailing arm which mounts to the chassis in front of the wheel and can move up and down (in coordination with the other side of the car, as this is a simple suspension and the two sides are connected). The up and down movement is controlled by the spring and shock. If you add the necessary spring/shock changes to produce a 6 inch lift, the wheel hub again can only move in the arc constrained by the trailing arm, which will cause the hub to move both down (= your lift) and forward, creating conflict with the front of the wheel arch. Even if you're willing to trim the fenders, you'll notice that in the rear of the car the wheel arch in front of the wheels quickly becomes the rear doors, which you most likely want as you commented previously on maintaining heat and A/C.
As with most front wheel drive economy cars (and the basis of the Leaf was certainly an economy car chassis), the suspension is designed to be cheap and reliable, but not easily modifiable in the way you want.
I've never looked under a Juke so can't offer direct experience. I suspect that it's similar to the Leaf in the sense that it's basically an economy front wheel drive chassis lifted a bit to make consumers feel like they're tough and hip. If there is an all wheel drive version (I don't even know if there is), the rear suspension will (generally speaking) be more similar to the front of the Leaf than the rear of the Leaf, in the sense that you'll have independence between the two sides.
If this is something you want to pursue, and if you don't put much value (= value lost) in your Leaf in it's current functional configuration, then by all means go for it. I don't think you will reach a 6 inch lift by simply removing Leaf suspension components and replacing them with analogous components from a Juke or other Nissan vehicle. I think some fabrication will be required to get that kind of lift.
You previously mentioned 31 inch tires. An alternative to trying to lift the Leaf considerably would be to widen the track with different wheel hubs or wheel spacers. Let the tires provide most of the lift and move them further from the body to help with clearance. You'll probably still have to hack the fenders up or away, but this would be faster and likely cheaper than trying to significantly lift a Leaf. You'll probably still face steering issues, and when you start moving the wheels further out with spacers you also run into rapid degradation of other components (e.g., wheel bearings), but that's a relatively small concern in your equation at the moment.
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