With Neovim's provider infrastructure, the unnamed (*) and plus (+) registers can be securely sent to an SSH account that uses a shell specifically for storing and retrieving the clipboard. The purpose behind this is to allow you to have access to the same clipboard data across multiple computers (ideally in a closed network).
It works, but is very much not production ready. This will be updated with more information later.
If you want to try it, look through bin to get an idea of how it works.
cshell is a C version of the server script, it has a script for setting up
restricted user account for sshclip.