Just two small comments on this straightforward document:

— Section 3 —

 Figure 1: ECH SvcParam with a public_name of "ech-sites.example.com"

The example actually encodes example.net, not example.com
[This was a test to see if we check these things, right? :-) ]

— Section 4 —

   These servers SHOULD support a protocol version that is compatible
   with ECH.

Why is this not a MUST?  What might be a reason to publish an ECH record for a server that doesn’t support ECH?