Updated list of remaining issues according to Closer-to-MOP
COMPUTE-EFFECTIVE-METHOD returns a function object, not an effective method form.
Multiple slot options are not passed as lists to DIRECT-SLOT-DEFINITION-CLASS.
The automatically created accessor methods in DEFCLASS forms don't call SLOT-VALUE-USING-CLASS and (SETF SLOT-VALUE-USING-CLASS).
Out of these, please correct me, but the third one is probably bogus. If the class is a standard-class, ECL is free to generate accessors which follow its own protocol, since the user is not allowed to extend slot-value-using-class (the type of the class should not be an specified one).
In the last days, METHOD-COMBINATIONs have finally been implemented and are used in ECL, which now uses the specified dispatch protocol, honoring COMPUTE-APPLICABLE-METHOD-USING-CLASSES and COMPUTE-APPLICABLE-METHODS. The only missing part is the COMPUTE-EFFECTIVE-METHOD part, but it should be fixed soon.