I've been asked how one might have a private wiki conversation with a select group of individuals. I accepted that this was an important use case, say for use inside an organization. I explained how I used firewalls and VPNs.
There are more interesting solutions.
Throughout development kind folks have brought related mechanisms to my attention. See Related Federation
Two are especially relevant.
Zooko Wilcox-O'Hearn and I have have expressed a mutual interest in seeing federated wiki and the Least-Authority File System, Tahoe-LAFS, work together.
Ryan Bennett has demonstrated federated wiki integrated with the client-side implementation of Named Data Networking, NDN, a version of PARC's CCNx.
Ryan's work represents extraordinary effort since communications between the client and server in the version he used were in a tangle we have yet to fully rationalize. Both LAFS and NDN integration will be much simpler when we realize Three Layer Storage.