@tomw most of these complaints are non-issues if you think of the directory as a centralised service.
But by trying to make it look like it might be decentralised, it seems to have worse privacy than a simple centralised user database would have.
You can enumerate every account, including deleted accounts. You can also see the full username change history of every account. It seems like a great trove of information for research, but I'm not sure users are aware that it is being published.