Some systems already have a solution for this, since devices can have multiple IPv6 addresses at once. They have one permanent IPv6 address which is not used fo

Some systems already have a solution for this, since devices can have multiple IPv6 addresses at once. They have one permanent IPv6 address which is not used for outgoing connections but can be used for incoming connections, and then temporary IPv6 addresses used for outgoing connections which can be rotated arbitrarily often. The first address is permanent but can only be used if you already know it. An improvement on this would for services to request the machine to hold a specific address, permitted if the address is valid on the current network and not already in use. Then services could each have their own address (generated on first use and then requested when they start) which is effectively permanent but not the same as the addresses used by other services on the same machine.