The probleme here is, that for this functionality, you need to have a listening server at your bitcoin-core and opened a specific port in your firewall, and port forwarding enabled if you have a router and want this to work over the internet (and a static IP address or dynamic DNS).
The integrated tor hidden service support could be pretty helpful here...
Can you please discuss this with Luke Dashjr..?
He seems to have some plans for this...
ZeroTier was also discussed on Twitter..
I personally don't have a clue, but I think you may find this discussion interesting:
https://twitter.com/adamierymenko/status/862755716565655552