@geynard, you are correct that our approach doesn’t work for every NetCDF dataset.
It only currently works currently if the compression and filtering schemes used in the NetCDF file are also available in the numcodecs package, which Zarr uses.
And it only works performantly for specific use case if the chunks are a reasonable size (10-200MB) and have appropriate shape. For example, nothing will allow you to efficiently extract a time series from a (time=20000, y=4000, x=4000) cube of data if your chunk shape is (time=1, y=4000, x=4000). (See Read multiple tiff image using zarr - #2 by rsignell)