Yeah, I see that point too and have thought about it (not just in the case of Scout), but there are several developed engine designs that can be licensed. Scout has three years ahead of them before launch. They have not said the EREV will launch at the same time as the EV. They can plan for it...
I'm hoping Scout does this right and uses a clean sheet design for the engine and generator. I hope the plans are not to repurpose a corporate VW car engine. Powering just a generator can allow for a more efficient combustion cycle and lighter weight engine to maximize heat loss.
That is what so many people did not understand about the Volt. It was a near-pure Series hybrid. The engine was rarely called upon to power the drive wheels. A beautifully engineered machine.
Let me help a bit. Hybrids are divided into two architectures: (a) Parallel Hybrid and (b) Series Hybrid.
Parallel means the gas motor (it can be gasoline or diesel) runs in Parallel with the electric drivetrain to power the electric motors and charge the battery and has a mechanical connection...
The way I see the range extender is a series hybrid similar to the GM Volt but without mechanical connection between the engine and the drive wheels through a (planetary) gearset. The Volt could drive entirely on the gas engine/generator and recharge the battery along with powering the electric...