Much more like the Chevrolet Volt.
It would be easy to control with the engine off, but while the engine is running the generator would need to be speed matched, or a CVT transmission required to match the output.
There is only 1-2" between the two motors IIRC, so really only a rigid coupling would fit which would not work.
The solution implemented, while not the most efficient, is the simplest to implement and works well. I bought mine with ~3k miles, up to 40k now without major issues. Love the truck, and hopefully I get a lot more time with it as it seems PHEVs are not getting the OEM attention they deserve.
Saw another one just sell on eBay last week for $24.5k. It was definitely one I had seen for sale previously though, probably from someone posting here if you look through the thread.