Hi, In https://github.com/dask/dask/issues/5526, we're seeing an issue stemming from a hack to ensure compatibility for Pyarrow. The details aren't too important. The core of the issue is that the Pyarrow parquet writer makes a couple checks for `FileSystem._isfilestore` via `_mkdir_if_not_exists`, e.g. in https://github.com/apache/arrow/blob/207b3507be82e92ebf29ec7d6d3b0bb86091c09a/python/pyarrow/parquet.py#L1349-L1350 .
Is it OK for my FileSystem subclass to override _isfilestore? Is it considered public? Thanks, Tom
