> now they need to try every possible private key to see if they can open our encrypted SNI.
The idea was to have a single common introductory keypair which all tenants publish to their DNS, in order to encrypt the SNI. That way there is no need to try multiple private keys.
The lack of DNSSEC deployment is an issue, although there's nothing to stop such schemes being employed on an opportunistic basis. However, when DNSSEC is available for a domain, the scheme should be enforced to prevent a MITM attack.
Two small problems I will mention, one of which I'm sure you already know: First, encrypted DNS and DNSSEC are not yet widely deployed, so this isn't the silver bullet many people expected of Encrypted SNI.
Second, for an endpoint which has many unrelated names and certificates - which is the case where encrypted SNI is gaining us a clear security benefit given our packets must have a plaintext IP destination - now they need to try every possible private key to see if they can open our encrypted SNI. This might be a very considerable burden.