Using an any object as the default value displays a JSON version of that object. This might not be very user friendly.

Here is an example using IPv4 from ip-num package:

(default: {"bitSize":32,"maximumBitSize":"4294967295","type":1,"octets":[{"value":1},{"value":1},{"value":1},{"value":1}],"separator":".","value":"16843009"})

Consider changing JSON.stringify at https://github.com/tj/commander.js/blob/master/index.js#L1413 to a scheme utilizing .toString instead. The impact could be pretty severe though.