The ban is just going to stop you registering a gas/diesel vehicle newer than x. So if the ban comes into effect in 2030, it will be impossible to register a g

The ban is just going to stop you registering a gas/diesel vehicle newer than x. So if the ban comes into effect in 2030, it will be impossible to register a gas/diesel vehicle that is a 2030 or newer in said state. Sure, you could register a vehicle in a state or country you don't live in, but that's already illegal.