I mean you do have to live close to a (tri-)state border to pull this off, but it’s probably doable.
As a reminder, we’re talking about a (hypothetical) 183-day rule for car registration here (as opposed to the ~30-day one we currently have, which makes loopholes that we discuss here absolutely impractical).
The administration has gradually modernized so that all the legal requirements of tax/registration/insurance can be checked online.
However, there's a loophole that's apparently becoming popular: "ghost plates". Number plates aren't a secure document. They have no authenticity markers. So you can just.. print your own, slap them on, and you're very unlikely to get police attention. A subset of that is plates which are IR scattering so they don't show up on speed cameras.
We don't call fake IDs either a loophole or "ghost IDs". When presented as identity documents, they're fraudulent identity documents. It doesn't matter if that ID is being presented to a bouncer in order to get in to a bar, or to everyone who cares to look at your car's bumper while it drives down the motorway, it's still a fake ID.
Only these are "ghost plates". So called because the letters appear faint, or ghost like, on ANPR cameras.
Using illegal plates, either ghost ones or cloned ones (where they're real plates but for the wrong vehicle) are not loopholes, any more than breaking into someone's house and stealing their stuff is a "loophole" for property ownership.
Pretty sure that's illegal, no? You have 30 days after bringing a car into the state to register it with the CA DMV.
It’s not 30 days it’s 20 but it isn’t “bringing into the state”, it is becoming a resident of the state, and that has more requirements than just showing up for a month.
Considering that half the parking lot of my building was out of state plates, it seems like it's not a huge concern for anyone.
It's mostly a voluntary standard for convenience. You can still get 5.5" x 9.5" plates in Delaware.
Functionally, that's what already exists - the standards are dimensions and readability. There's no CA smog inspection station as you enter the state, this is about people abusing a loophole. I spent all 4 years of college in CA with a CA driver's license, a car with out of state plates, and zero Kafkaesque issues. Maybe tax avoidance loopholes are Kafkaesque because they're not how anyone is supposed to do things.
As one more wacky way to do it, some countries rivet the license plate to the car because the plates never change. They're basically shorthand for the VIN, so the owner and their place of residence don't matter, only where the car was first registered.