Registration plate lookup would be a chicken/egg problem here in the States. You need proof of insurance in order to get your registration, so on a vehicle that has no plates, there's no number to give, so wouldn't be able to get insurance. VIN is really the way to handle it, and once you get through the "quote" stage to actually buying it, all the insurance companies can take any VIN (and your info, of course) and spit out how much it actually costs. On a state by state level, I don't imagine it would be difficult to build a system to accurately compare rates. The fact that each state has its own system of minimum requirements, as well as what can be covered, and insurance companies are isolated to a single state (the larger insurance providers are actually corporations with wholly owned subsidiaries in each state) increase this complexity when dealt with on a national level. It's extremely similar to the issues with comparing health insurance plans.