Ask HN: LinkedIn, but only for people you've physically met?

I keep getting requests for an intro with people who are my LinkedIn connections, but I don't actually know them.

I'm thinking of an app that would generate a unique QR code, but the person scanning has to be in the same location. May also need to take a selfie together. There seems to be additional value in making it a little more complicated. This means you really should have a good conversation with each other and want to stay connected, so both have a more exclusive connection.

You build a network like that -- you have a guarantee that all the contacts of someone you have met that are in this network actually know them, or at least met them once.

Am I missing any obvious things? Any technical difficulties? How could you hack this system for verification?

Thanks!