I've long wanted something like this for addresses or contact details. You register your address somewhere, and give access to it to companies by signing their

I've long wanted something like this for addresses or contact details. You register your address somewhere, and give access to it to companies by signing their certificate. When you update your contact details, you do so in one place and it sends a notification to each organisation to update their details. It'd be better as well if you could revoke your permission with that company so they can't contact you.