Hosting service A shouldn't mean that every user of service A can also figure out you host C, B and D.

Also, the IP protocol does not care about ports at all. Ports are a thing for UDP and TCP.

> Also, the IP protocol does not care about ports at all. Ports are a thing for UDP and TCP.

You're right, they are one level above.

> Hosting service A shouldn't mean that every user of service A can also figure out you host C, B and D.

It how are ports on a single IP address essentially different from multiple IP addresses within a subnet?

In a /64, enumerating all hosts will not be as practical as enumerating all ports on a single IP. Further, you will not be able to link that two services are running on the same host by just the IP.