In the UK the license plate will only give the address of the registered owner. It doesn't include any phone numbers or anything about the next of kin. It doesn't include a photo, either, and the registered owner may not be the driver.

A neck tag is fine if you like that sort of thing, but many of us don't like wearing stuff around our neck. Also, I'm not sure how effective it would be. Often first responders are reluctant to go ferreting through your personal possessions in case they get accused of theft. The windshield thing is supposed to be easily visible, obvious in intent, and accessible.