Perhaps we should just recognize the fact that SMTP does not really
support mailing lists, it never has and never will. All the kludges and
duct tape in the world won't fix what is broken here.
I read my IETF mail through gmail because, well its easiest to do that. And
I have roughly 10GB of mailing list traffic. Most of which is probably
copied 50-100 times or more.
A much more efficient approach would be to use SMTP to submit the mail and
some other protocol (POP3, RSS, IMAP, something new) to retrieve it.
Protocols do wear out and at some point it is easier to start from scratch
Build in end to end encryption while we are at it.