It is an interesting questions, if with a modern user interface, can they get to new life?
I see no reason the state of the art from the legacy remailer types can't be combined and updated into a new service running on some of the same relay machines we have for Tor today. Even if only 10% ran them it would probably be more hosts than were ever behind the old remailer nets. And relay operators already have the abuse experience in place.
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