Hi, EV aerothermal CFD engineer here. This looked like a fun place for my first post. Wow, where to start with this. CFD pet peeve: streamlines in isolation aren't engineering, they're PR fluff. Yes, a sufficiently large hole down the center of the car could decrease drag, but you'd be far better off just making it less wide! (Yes, ducts generally add drag, but that's because you're catching the air and accelerating it up to the car's speed, or nearly, and then dumping it. This thing is attempting not to do that, but will still be inefficient.) External downsizing, specifically on the sides, is what Elio and other pod-cars did, in the extreme. I wouldn't call them a "successful car company", I'd call them a niche manufacturer finding just enough oddballs(/optimistic investors) to stay alive. (Not that there's anything wrong with that.) All modern car designs are shrunk as much as they can to decrease frontal area to the limit of impinging on the occupant space or style intent. Punching a hole through the middle is just heavier for the same result. Being larger and having no structure through the hole area it must necessarily be heavier to be structurally sound. Weight is also critical for efficiency of course, especially with city driving or inclines. There's a reason twin-fuselage airplanes haven't become the norm, and only exist for very specialized uses: https://en.wikipedia.org/wiki/Twin-fuselage_aircraft
If he tried to make these from existing cars he'd find they're tightly and deliberately packaged with stuff in that area he wants to blow a hole through. In that Tesla specifically there's a center radiator, ducts, suspension and steering components, structure, *battery pack*, MOTOR!, huge HVAC unit and ducting, nevermind cargo and passenger space. There's nowhere else to put this stuff without just making everything about this idea even worse. Ironically enough, that Mercedes concept demonstrates that you can achieve a far better result managing the air outside the vehicle; you don't have to bore a hole through it. That concept isn't going into production because it'd be crazy-expensive but movable bodywork is increasingly on the road as they learn to make it cheaper, lighter, and reliable. It's usually more of a style thing as the aero gains just aren't huge without unmanageably huge mechanisms. And a tunnel you could ride a scooter through qualifies as an unmanageable mechanism!
The reason the drag is reduced compared to the Tesla S (which has great aero for its size) is that it simply isn't a comparable vehicle anymore! You can also strip out all the interior, cut off the roof, and replace the windshield with plexiglass to make a lighter and therefore more efficient car. But it isn't remotely in the same category of car anymore, and you could design a superior lightweight car from scratch than you will ever get by mangling a well thought out design after the fact. With a couple hours' work I could run CFD on a car shape, then again with a big hole down the center, but I won't because I can tell you with confidence that if you make the hole big enough it'll have less drag. This isn't a new idea, it just isn't applied at this scale because it makes a bad car.
There are countless practical reasons not to do this (and more why noone would buy it), but more to the point, this isn't a company, this is some rando with an undeveloped idea, access to (some form of) CFD, a loose grasp of video editing, and a YouTube account. I am certain this video exists only to drive clicks to those spam-y "partner websites". It's pretty hilarious he's offering options like a bed (#vanlife) and suggesting "get one today!" This is not the cart before the horse, it's a flaming cart tumbling down a mountain like a crashed car in an action movie. There never was a horse.
Car moves through air... air hits car and "wastes" energy... remove car and energy is saved!