@evolve-0
I don't see that being a problem. No matter how the random number is generated, duplicate address detection is used to avoid collisions. As long as there is a 64 bit random number, it's actual value is irrelevant. If it matches with an address on a different subnet, so what? The prefix will be different, so the address will still be unique.
I think some people worry too much about "privacy". While there may be some concern about tracking people where they go through their MAC address, there's no reason to worry about it for the stable address. It would only be used for reaching a computer, so the address must be known. If it's always in one location, then there's nothing to track. Further, once you're off the local network, there's no way to tell if it's a MAC or random number based address.