Thanks for a clear document specifying a useful extension.  And the appendix of examples is a great help.  I think the draft is ready for approval.

I do find myself wishing that Section 3.3 had been done as a bullet list to avoid repetition, somewhat like this:

———————————
   The server MUST return a FORMERR response in any of these conditions:
      * an MQTYPE-Query option is received in any inbound DNS message with
         an OpCode other than QUERY (0)
      * an MQTYPE-Response option is received in any inbound DNS message
      * more than one MQTYPE-Query option is received in a query
      * ...etc…
———————————

But this is a style preference, and I don’t expect nor ask for changes at this stage.  Carry on.