I've also been thinking about that! I wonder if https://archive.org/web/ is an alternative though, as in could I pay them so they could mirror it for a 100 years?
I would absolutely love to be able to donate a domain name to the Internet Archive plus a lump sum cash donation and have them keep it hosted in perpetuity.
Sign me up too, I've got a (very small) site that I would like to outlive me; my plan is to attempt to set it up with a large balance at NearlyFreeSpeach.net and also put the account identifier in an HTML comment so that motivated people could increase its balance in the future.
I would be very interested in other credible perpetual hosting plans.
