The Wagoneer is expected to see the light of day sometime around the next Durango refresh. Which could mean the Wagoneer shares its underpinnings with the Durango/Grand Cherokee family. But its not so simple as slapping a new body on a longer WK2 platform.
Its also been rumoured that the WK3 series (GC, Durango, maybe Wagoneer) MAY, and I STRESS the MAY here, transition to a car based platform which sounds like it could be consolidation/harmonisation with Maserati's work on the LX platform, meaning the GC, Wagoneer and Durango could all be using a derivative of the Maserati Levante's Ghibli based platform.
Heavy suspension work would need to be put in to make that platform Trail Rated, but that should be of little consequence, as the current Durano/GC share a platform but no similarity in suspension. It's believed that the transition from WK2 to WK3 will be substantial.
Rumors are now flying over whether Grand Cherokee, Wagoneer, and Durango will continue on their own platform, or switch to an LX-based (or D-RWD-based) setup. They would likely keep unique suspensions but change their core dimensions and architecture to reduce costs; Maserati and Alfa Romeo are both working on car-based crossovers, so the form factor is being developed regardless.
Or in other words a modular/scalable RWD platform, similar to VW's MLB/MQB system, as a way to fight costs and extract more margin.