Alt energy? A rig with a diesel powerplant that could handle biodiesel fuel and had a driver-controllable idle stop/start setup -- so if you're off road you can turn it off if you want -- would be "alt" enough of a 4x4 (or at least one I'd go for).
Of course, I'd even go for that Steam-power augmented gas engine design that BMW developed a few years to make power out of typically wasted engine heat.
The steam from it is used to generate electricity for an electric motor that augments the vehicles power
But for off-road vehicles you do a "Mr. Fusion" type thing with the steam setup: you set it up so that an onboard source other than just the diesel engine -- say a "firebox" in the back of the rig -- lets you produce heat from wood or whatever combustibles you can scrounge up in the boonies. Maybe this lets you produce steam and then just enough electricity for an electric drive motor on the rig such that it could get you back to the nearest diesel station (when you're on empty), or otherwise let you stay out in the woods (whether you have enough diesel or not).
Of course you'd need to add water periodically to some kind of steam setup which is why the rig's roof would also have a rain catch and fresh water/salt-water processing capacity also
All this doesn't seem "environmentally friendly," but it might fit the bill for people in or heading to sparsely-settled, developing parts of the world that have few diesel stations, but ample forests that can spare a dead tree or two.
