As described in ODATA-1450, when we create a resource we can link it to other, existing resources using @odata.id. We can also create new related resources.

This is similar to what we do with a delta patch operation and, indeed, within a delta patch operation we can create a new entity and create/update/remove related nested entities.

Should we support the same functionality when creating a single resource (i.e., using POST) that we do in a delta update?

Specifically, when we create an item using POST, should we
1) Support referencing existing items by key properties as an alternative to @odata.id? Note that, for non-contained nested resources with no navigation property binding you would have to either include the @odata.context in addition to key values or include the @odata.id.
2) Support modifying properties of related existing items?

Same question for using PUT/PATCH as an upsert – seems like at least PATCH, which already supports keyvalues and nested deltas for update, should also support the same changes as part of a create.