(Please tell me the actual thing does not have up/down "like" votes; that's completely stupid in a mail archive (not to mention misleading), and preventing abuse of it would require visitors to be authenticated, which is also a complete stupid thing in a mail archive.)
The web page has a link to some dated mock-ups (2012):
https://wiki.list.org/HyperKitty
It looks like some random web BBS forum.
(Please tell me the actual thing does not have up/down "like" votes; that's completely stupid in a mail archive (not to mention misleading), and preventing abuse of it would require visitors to be authenticated, which is also a complete stupid thing in a mail archive.)