Looking at this photo as an engineer, I decided to have some fun and see if there’s a way this design could somehow be a unicycle after all, based on no prior knowledge.

Supposing that maybe the two wheels turn independently, this just ends up being topologically identical to the so-called hoverboards. Except that hoverboards are configured with small diameter wheels and set to a wide gauge, allowing them to make zero-radius turns without scrubbing (aka tank steering). But this contraption, with its large contact patch and narrow gauge, would surely scrub quite hard for zero-radius turns.

Ok, so that doesn’t really work. Maybe it’s a solid axle. But… that’s somehow even worse since its performance is nearly identical to a single, wide tire. The Onewheel skateboard is proof positive that a single, wide tire is valid, but the crucial aspect is that the Onewheel still banks like a bicycle or airplane, rolling onto the edges of its tire. So too must this Inmotion unicycle, but then the outside tire is less involved in stabilizing the turn.

The only example I can think of where it’s beneficial to split one large contact point into two smaller ones is at sea, where a catamaran uses two parallel hulls for its hydrodynamic benefits. And for sharp turns, one hull lifts entirely out of the water, which is desirable. Whereas lifting a wheel off of land is not.

I can only see downsides with the dual wheel, solid axle unicycle design, reminiscent of this video by Practical Engineering on rail wheels (Nebula or YouTube). In short, optimizing for stationary stability means giving up dynamic stability while in motion, either inhibiting a turn or turning uncommanded. Trains use solid axles with conic wheels for dynamic stability and rely on truck/bogie geometry for stationary stability.

TL;DR: I can’t come up with a good reason for this design

Yeah, seems like it can’t be a unicycle if it has more than one wheel