Pipermail is part of mailman 2, which is the about to be deprecated very soon version (it's python 2 only).
Mailman 3 has a different thing, but I haven't tried it yet.
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.)
It is infidelity inspired by the layout of a forum, but looks great IMO.
Lurker wipes the floor with Hyperkitty.
(And is fast: C++ that generates static pages!)
I had no issue with this with Lurker. A few times in the (now fairly distant) past I gone in there and blew off all the generated content (after editing an mbox archive file), then re-generated.
Since then I developed an invisible delete button right in the web UI, for removing spam from the web archive. If you know where to click, and what the password is, you can blow off any post.
An archiver that can't import your historic mbox files has a showstopper issue for anyone with existing archives, and may present a problem to someone who wants to rebuild a damaged web archive.