I have over 10 years of aviation maintenance under my belt and landing gear is one of my specialties. I see a problem with traction under certain conditions..this is only going by the images provided. On most aircraft the nose gear is purpose built for one thing, steering while taxiing. And sometimes they struggle with that. The weight distribution of the aircraft is not equally split between the 3 gear. The 2 mains can acount for 80% or higher of the aircrafts load. If it's running on the apu alone you are negating thrust provided by the engines which in turn reduces pressure/weight to the nose gear. This would reduce the contact patch of the nose tires, which will reduce traction (on tires that are basically slicks). This would be almost impossible to install in the main gear. There are huge stacks of brake plates in it..no room. At most, I see this used to back an aircraft away from the terminal..not cost effective. We'll have robtic dollies before these are installed. Nice idea, but I won't hold my breath

Wait, your going to let a 737 pilot back up the aircraft without even the benefit of a rearview mirror?....
Of course not, the ground crew will still be out there spotting. And normally the tugs are hooked up before the jetway is pulled away from the aircraft....
And what about the batteries required to get 66 metric tons moving from a dead stop as many airports require the aircraft to be pushed away from the gate before starting their engines....
I’m not sure flying around that added weight will be worth that seven minutes per flight....
This thing may be more useful in assisting forward movement of the aircraft on the taxiway in larger airports where it takes a while to get to the gate, think LAX....

Is not the weight a concern?

From the layman's point of view this seems like a "eureka moment." Like, "why in the hell hasn't someone thought of this before?" Those little tugs puffing all that black smoke are clearly polluters; but maybe with all the JP4 fumes around the airport, eliminating the tug-diesel-exhaust wouldn't be much of a benefit. At first glance, though, it is a very cool invention.

If it really saves 7 minutes per flight it will be worth every penny to an airline like Southwest. Not really sure how they come up with 7 minutes, I mean the truck is hooked up to the airliner before the door closes, and the pushback would be the same time, and it only takes a minute to disconnect the pushtruck? Or am I missing something?

This is probably made practical by much lighter electric motors and large onboard battery capacity. Very little power is required because of the low speed. Don't have to wait for push truck to clear area.

I am an investor in Wheel Tug. I will try to answer some of the questions posted here.
1st, the nose wheel has enough traction at least 95% of the time. Under rare conditions of icy and some uphill, the plane can revert to what it always has done and use the main jets to taxi. The problem of putting an electric motor in the main wheels is basically heat; that is where the brakes are.
The system discussed here will have a 360 degree camera options for situation awareness.
The time savings are very real and documented. More savings can come from letting passengers us both front and rear doors. Jet blasts mostly prevent such a process now.
Other significant savings come from the main jets not sucking up debris. There are also costs for the tug tractors and more often than is generally known, the tractors damage the plane or push it into something.
About 1000 planes are already signed up to add WheelTug (WT). The FAA has approved a plan for the testing that will be needed to certify the system.
The expectation is that airlines will eventually save over $1M per plane per year with WT.
The pollution from main jets running while on the ground is even more important than that from the tractors. There is also a noise issue and safety enhancements. There are now too many injuries to ground personnel, including from jet blast.

I'll bet whichever labor union the tug drivers belong to is gearing up to try and stop industry adoption of this.

If the engines are not turning when passengers are boarding then little old Japanese ladies won't throw coins into them for good luck -:)

This is the first implementation I've seen of the idea of using electric motors for taxiing, though the idea itself is much older: The professor of the engineering department at college back in the '80s suggested just this idea, though no doubt there were others before him.