tl;dr: the original site went down (apparently abandoned), and a replacement was uploaded at https://blueprintnotincluded.com/. Since it was a new upload, it doesn't look like they were able to migrate existing blueprints.
I saw that the domain expired, so I picked it up. I'm considering an alternative implementation, with (IMO) better organization, search, linking, etc, since there were some pain points with the original site. If that doesn't happen, I may just redirect to the new site. TBD.