Yep - you caught us. We weren’t expecting Code42 to do what they did so didn’t have anything prepared for CrashPlan orphans. 
You are correct, Duplicati is designed for local or cloud based backups and does not have any P2P (peer-to-peer) functionality built into it at this time. However, your situation sounds very much like mine - lots of family were backup up to my server with CrashPlan.
Since it sounds like you’re using a Linux based server I’d suggest looking at something like this:
Basically, anything you can expose on your server that looks like any of these, will work as a destination:
- S3 (such as Minio)
- WebDAV (such as OpenCloud or NextCloud)
- FTP
- SFTP
As a non-centralized tool, Duplicati doesn’t have the kind of reporting most CrashPlan users are used to, so you may also want to check out DupReport:
Lastly, as on OpenSource project anybody is free to contribute to the code base over on GitHub - so if there’s a feature you REALLY want to see, you’re welcome to work on it yourself or entice others to do so with a Bounty.