I suggested something similar here: https://discourse.joplinapp.org/t/any-suggestions-on-what-web-technology-could-be-used-to-add-support-for-sharing-notes/10145/44
The idea is to share notes including their unique id and metadata in such a way that they can be imported into another Joplin instance resulting in an exact copy of the original one. In case the receiving Joplin instance already contains a note with an identical id, this would allow to use the same machinery to resolve conflicts like it is done with synchronization targets.