Reflections on module design

I believe that behavior of this module could be achieved like this:

1. Create new content type ContentType.
2. Create new entity type ComplexFiledType (field collection).
3. Create new reference field reference that links ContentType and ComplexFieldType.
4. Require reference field to links ContentType node with only 'dedicated' ComplexFieldType entity. That is, ContentType nodes CANNOT reuse ComplexFieldType entity that exists and belongs to other nodes. ContentType nodes must create ComplexFieldType entity that belongs to them and only them.

I also believe that point 1, 2 and 3 are easier to achieve, and point 4 represents some efforts into References module. At this moment References works with nodes and users, but not with entities. Some work on widgets needs to be done to accomplish behavior proposed in point 4.

The whole advantage seems to be more flexible module that reuse existing functionality like References, Views (relationships). I mean by using references one can link to many entity types (ComplexFieldType1, ComplexFieldType2, etc.). (Views module still makes use of fields so it's not the problem.)

Field collection is fixed so I couldn't find a way to have different field collections applicable to the same field.