I think if you feel nostalgic for something, then it has some seed of intrigue left in it. For guestbooks, I wonder how you might innovate them…

One thought I have is—sometimes I get Webmentions to the root page of my site. I might make a ‘guestbook’ page that list any comments or links sent by Webmention there. (I do think that the Facebook ‘wall’ was a modernization of the guestbook—wasn’t it? Although perhaps that functions more like a public e-mail message.)