They have to be very, very careful with the control software, or this system will be dangerously unstable at highway speed. I am an engineer, and I had this idea in 1992. After studying it for awhile, I came to the conclusion the liabilities would not be worth it.
The problem is uncontrollable secondary feedback. If anyone remembers, Mercedes attempted some years ago to produce a self-leveling industrial tractor-trailer ("semi") for use on sloped European roads. After some testing and realworld miles, drivers refused to use it because the entire trailer would start oscillating uncontrollably.
Nice idea, but I doubt the algorithms are sufficient for this application. It does merit study and development however, since it would be a great idea if it could be made to work safely.

Eventually all Semi truck trailer combo's will be electric as the additional power plus storage plus safety issues will surmount any other types of locomotion (e.g., diesel with stupid 8 wheel drive). computers are so fast today that the tandem electric semi and electric trailer will make jack knifing a thing of the past as they can instantly vector torque to each wheel independently and apply either power or braking to make sure the tractor trailer stays in a straight line. I completely disagree with Malatrope and I too am an engineer--mechanical engineering degree (actually 4 degrees--chemistry, ME, Wood Science & Engineering and Math).

I agree with VincentWolf, the progress of computer control since Malatrope's 1992 attempt is staggering.Who would in the 1990's have believed the science fiction that predicted today's reality? I worked with hydraulic activated robots built in the 70's with circuit board cabinets the size of wardrobes. Now a million more information is held in chips too small to see without a magnifying glass and speeds only geeks thought possible.

Many random thoughts here; handling issues aside, how will this trailer/vehicle be viewed by the government for purposes of taxation and registration? What exactly is it? I'm sure, politicians will figure it out, lol. Secondly, the idea of reducing towing resistance seems almost intoxicating for those who know the feeling of dragging a heavy trailer over a mountain pass, but just wondering about the capacity. Some mountain passes are really long. If the battery charge is depleted long before the uphill segment is completed, the tow vertical is now hauling a lot of additional dead-weight over the pass and having to break for it going back down. If the intent was to enable smaller tow vehicles -- that's not good at all! But it does raise the option of additional braking using a regen mode - that wasn't mentioned on this particular product unless I missed it. It also adds options maybe never before possible - anti jackknife perhaps? Anyway, using this tech to lower the tow vehicle size or rating, sounds like playing with fire. However, using it on very low settings, to reduce fuel burn in certain operating parameters, sounds interesting.

I can't wait for the drive package to be made available for every other trailer.
This seams like the way to make trucking go hybrid. Making a big truck hybrid just isn't catching on.
Technology and sensors are finally catching up with the performance needed for this to work.

This is awesome... I'd luv one for my model 3...it IS the future and how they can make it work... Also like the idea of a pop-up style battery extender trailer... To extend range when needed for getting away from it all... And this also could bluff into the home micro grid and add to the Tesla power wall concept! Poly battery use dramatically increases the value of these products... Awesome forward thinking

This might work well with a hybrid power train, particularly one with “electric only” traction. (Something like the Chevy Volt) Alternatively, if it were equipped it with its own engine driven generator, one might be able to tow it using a purely electric car, with the trailer engine being used to charge both. It’s not zero emissions, of course, but would be much less intrusive than the giant pickups and such often used to tow RV trailers these days. It’s true, though, that in any case, the control system for the axles would need to be very, very carefully developed.

I have always wanted a bicycle trailer that follows without resistance. This virtual weight reduction sounds good, but what about the wind resistance and tire drag?
[You might want to check out the powered Ridekick bicycle trailer, which actually pushes cyclists along: https://newatlas.com/ridekick-motorized-bicycle-trailer/20953/ - Ed.]

For a lot less money they could have just made it lighter and aero to achieve the same goal. KISS And I hope the battery weight is concentrated close to the axle.

This is actually brilliant but it's far from an original idea at all, this is pretty much just the reverse (inverse?) version of Slugs: https://en.m.wikipedia.org/wiki/Slug_(railroad) If they made some kind of universal hookup, then it could work the same way with a hybrid car with it effectively being the same as a diesel freight train... or in this case an Amtrak train.