Hi languagehacker,
this is not science fiction. It just shows you a way of implementing a serializer that works for all kind of models in Django Rest Framework.
"The best documentation is the source code" :-) . I use to read it but sometimes is really hard to understand what's going on. As you said the serializer does a lot of thing.
Correct. It's very easy to create a simple model serializer and this is what the general model serializer does. It's no big deal just saves a few line of code.
In Django Rest Framework (DRF) you need serializer class. Maybe this is because DRF is not tightly coupled with the models from Django framework.
As far as I know DRF does not support PUT/UPDATE operations for nested serializers. But there are cases when you just need to read. Like getting an activity feed which can't be modified directly by the users. I think if you have a good caching system it's better to return all the data for one request instead of creating new requests to get details about each entity.