Public review comment https://lists.oasis-open.org/archives/odata-comment/201710/msg00005.html

The document "OData Version 4.0, Part1: Protocol" specifies in section
"11.4.6.2 Remove a Reference to an Entity":

For collection-valued navigation properties, the entity reference of
the entity to be removed MUST be specified using the $id query
string option.

It would be nice if instead of or at least additional to using the $id query
option it would be allowed to use the key after the navigation property
to specify which entity is referenced.

Example:
DELETE http://host/service/Customers(1)/Orders/$ref?$id=../../Orders(4711)
could be expressed as
DELETE http://host/service/Customers(1)/Orders(4711)/$ref

This avoids a mandatory query option, handling of nested URLs, and parsing of relative or absolute URLs including verification that the URL is fitting; last but not least it is shorter and easier to understand.

Kind Regards,
Oliver Heinrich