Why leak your primary keys? They are for the DBMS, not your end users.

Primary keys to what? Users wanting to get a specific piece of data will need to know some user-visible Id for that.

You can masquerade internal Ids with opaque Ids if you want to maintain a translation layer. There's also more distributed use cases that require coming up with new Ids in isolation, so they will be "exposed" anyways as you sync up with other nodes.