This looks like the first serious attempt at a useable hybrid TRUCK. They look to offer all electric models (plug in - NO ENGINE), but 35-40 miles of range in a service truck seems pretty limited. Not HP limited with 400hp, but useability/range limited. I know of not a single contractor with a Van or Pickup that only puts on those limited miles in a day.
Their eREV version though is really interesting in that they have emulated your modern diesel locomotive and added batteries. They start with a more than adequate 4.8L V8 coupled to a 100,000 watt generator. The large engine allows for tons more power generation in comparison to the dinky hybrid engines, and this means that they can drive the electric propulsion motor directly like a locomotive does, as well as charge the batteries because they will have EXTRA power to do so. And, Liquid Cooled batteries allow for much faster charging.
GM's V8 technology has come so far on its own in both economy and durability, that this is a perfect combination of efficiency.... perhaps the best you could get with available technology. The V8 does not necessarily have to run at higher RPM except to achieve full AC power output, and computer control can allow it to run at more fixed RPM ranges that match the specific moments real need.
I like the concept, but I dont think I would like the price. It's going to be up there.