One missing feature/todo is the one of the important features that differentiates HDFS from many "academic" distributed file systems (including Ceph) is end-to-end data checksums, which are computed in client and stored on data nodes and verified in client upon retrieval.

Personally, I'd avoid any distributed storage systems without end-to-end checksums.

Another related mandatory feature is background scrubbing (periodically verify block checksums and discard corrupted replicas).