The current implementation of the WriteConcern object has a few issues:

• forces j to true/false
• forces w to 1 if undefined
• converts wtimeout to a number
• always sends all fields even if not set (defaults to values above)
• can't add arbitrary options
• validation is poor
• missing fsync support (not so important once we allow arbitrary options)
• doesn't inherit from collection if not overridden
• isn't settable on DB

This causes various problems as all defaults should be handled at the server, not client, and the client should be able to pass arbitrary options.