Add field collection "type" and expose those as field types in field_collection_field_info()

That sounds like it makes sense. Out of curiosity, what benefits would this bring?

trying to be more clear

If I understand correctly you want to be able to use a field collection with a structure that has already been set up in another entity, right? Perhaps your goal can be accomplished by using "add existing field." Is there something you would try to do that wouldn't be covered by this?

The only use case I can see for this is to reuse the same field collection structure multiple times on a single host bundle. The coupling between the fields and the field collection bundles is tight so this wouldn't be easy to implement. For that reason I prefer #2044309: any way to clone a collection structure as a potential solution. It would also have the extra flexibility of being able to modify the structure of one of these fields without changing all of them.