That doesn't work, as neither SNI nor the server_name field of the ECHConfig are allowed to contain IP addresses: https://www.ietf.org/archive/id/draft-ietf-tls-esni-25.html#...

Even if it did work, the privacy value of hiding the SNI is pretty minimal for an IP address that hosts only a couple domains, as there are plenty of databases that let you look up an IP address to determine what domain names point there - e.g. https://bgp.tools/prefix/18.220.0.0/14#dns