issue_comments: 697952300

@shoyer & @jhamman just to give you an idea, I aim to see open_dataset reduced to the following:

```python def open_dataset(filename_or_obj, , engine=None, chunks=None, cache=None, backend_kwargs=None, *kwargs): filename_or_obj = nomalize_filename_or_obj(filename_or_obj) if engine is None: engine = autodetect_engine(filename_or_obj) open_backend_dataset = get_opener(engine)

backend_ds = open_backend_dataset(filename_or_obj, **backend_kwargs, **kwargs)
ds = dataset_from_backend_dataset(
    backend_ds, chunks, cache, filename_or_obj=filename_or_obj, **kwargs
)
return ds

```

Where the key observation is that backend_ds variable must be either np.ndarray or subclasses of BackendArray. That is backend should not be concerned with the in-memory representation of the variables, so they know nothign about dask, cache behaviour, etc. (@shoyer this was addressed briefly today)