NFS works great over the open Internet, as long as you do it through a secure tunnel. I've been doing this for years as a way of increasing the size of the available storage in a VPS.
I've used both vtun and WireGuard for remote NFS. On a good day, I get 100MB/s to the NFS filesystem on my San Jose AWS instance (from Vegas) via WireGuard. Note: That was before CoVid-19. CenturyLink/Quest has since (stealthily) throttled my bandwidth down from 1Gbps to ~750Mbps.
