Montana person here. I'm on the other side of this trade: trying to buy cars in California[1] that I'm going to register in Montana. My experience has been that it's very hard to exploit this "loophole". I know that because even not trying to exploit the loophole. I have to jump through hoops to prove to a dealer that I really live in Montana. And then the car has to be either put on a transporter, taken to the border (or all the way to Montana), or driven by an employee of the dealership to the border. Then we have to get paperwork notarized by someone at the border that the vehicle really left CA. You also have to pledge in writing that you wont bring the car back into CA except for maintenance. I've had dealers in LA just plain refuse to sell me a car because I lived in Montana. So it was not in recent years anything like as easy as "put a Montana plate on it" <waves hand>.

The article calls the ownership entities "fake LLCs". They were in fact completely real kosher Montana LLCs. The issue at hand is that CA wants to disallow the case where the LLC is owned by someone who is a CA resident. That's not the same as "fake".

Finally, anyone from California should experience the Montana DMV (called MDT here). It's like checking into the Four Seasons compared to the CA DMV! You can phone them and they'll answer within a few rings and help you out. You can go down to their office at the court house and perhaps have to wait in line for 5 minutes, but perhaps just walk straight up to the counter. They will help you figure out vanity plate letters, endlessly checking whether ideas you have are already registered. I almost make up excuses to go to the DMV, it's so nice there. Montana also has a system of sponsored plates. There are about 100 of them, which allows you to choose a plate of almost any color, which is nice if you want it to match the car color.

[1] Why do that? Well there are 100X more cars for sale in CA, and the prices are lower.