I'd be happy to host the list at
firemountain.net, where a Mailman 2.X
instance has been happily running a few dozen public and private lists for
15-ish years (majordomo before that) (homebrew scripts before that).
No charge, no ads.
If the archives are available in mbox format (or something that can
be massaged into mbox format) I can import all of those.
I would also suggest that -- to future-proof this -- that multiple
people stash those archives and stash future archives as they accrue.
Given archives and a subscriber list, a mailing list can be reconstituted
anywhere.
Merging lists: if the consensus is that it should be done, I can
do that. (Whether that means the subscriber lists, the archives, or both.)
Attachments: that's also do-able if consensus indicates but I recommend
that they be limited to open formats, because delivering messages with
proprietary attachments is a quagmire even if all the recipients want
them. (long explanation omitted) Many years of experience indicate
that doing this and imposing a soft large-but-finite maximum message
size facilitates communication without overwhelming people.
And since someone will ask: I use mutt.
---rsk