It would be really handy to be able to initialize a xarray.Dataset instance from an already opened instance of netCDF4.Dataset. I have a lot of code where I'm already returning an opened netCDF4 file and this would streamline the process of hooking xarray into that.

It seems like the quick solution here would be to make NetCDF4DataStore accept a netCDF4.Dataset instance as filename, which would bypass the creation of a new instance. Thoughts?