IANAMechanicalEngineer, but do we need to worry about additional stress on the left dropout? The forces to which this component is typically subjected are the weight of the system and the tension of the chain. This device would seem to add an additional torque associated with driving the wheel via the pill-shaped peg that slides into the dropout.
This probably wouldn't be an issue for most bikes, but it seems like it's outside the design specs for any existing bike.
Having done e-bike mods in the past, rear-dropouts tend to be stronger than front-dropouts, and on any steel bike you can put a lot of torque on the front dropouts.
Only problem with rear-dropouts is accommodating the gearset, which they cleverly handled by eliminating the gearset; that will suck if you run out of power downhill from your destination, but will otherwise work fine.
That would indeed suck! I can see why they didn't incorporate a cassette body (and the chain clearance issues that would entail: basically everything they have on the right side now would have to be moved to the left side) but it does make the final product seem less like a bicycle. (I know, this is sacrilege to the fixie folks. Meh.)
I had another thought: maybe through judicious sizing of (front) chainrings and the freewheeling cog one could get something that could climb a hill? Will widespread adoption of this device encourage development of a front derailleur that can handle more than three rings?
This probably wouldn't be an issue for most bikes, but it seems like it's outside the design specs for any existing bike.