Though these details are focused on the UK/European version, there are some interesting key points of the hybrid tech they've implemented in this model:
The Transit Custom PHEV uses a series-hybrid driveline configuration, with the vehicle’s wheels driven exclusively by an electric motor, rather than by the combustion engine.
The battery pack is a compact liquid-cooled lithium-ion design located under the load floor
No idea how or if these updates are going to be brought over to NA but kind of hopeful based on what I'm reading. Range still isn't anything to write home about at 30mi but it might also be due to being a larger vehicle with an expected amount of cargo being hauled around.