We’ve recently landed code in boulder to add support for the draft TLS-ALPN validation method. This method provides a way to perform domain validation via the TLS layer without the issues discovered with the tls-sni-01/02 methods. This challenge type is available in both the staging and production environments as of July 12, 2018.
For those looking to test clients locally against a ACME server I’d recommend taking a look at the lightweight pebble server which already has TLS-ALPN functionality.
We’d also be very interested in people taking a look at the draft specification and providing feedback based on implementation experience. Any feedback on the document itself should be sent to the IETF ACME WG mailing list.