Enum support has been added in the upcoming version. This new version (should be released in November 2012) adds improved support for customizing output and input, and most importantly, supports reading JSON into a JVM that does not have the classes that match the JSON read.
This is done by reading the input into a Map of Maps representation, and retaining the appropriate information. These Maps (JsonObject's) can be manipulated by having values changed, fields added, etc. When this Map of Maps representation is passed to the JsonWriter, it write's the content back out, using the same IDs and format as the original input.
I am also looking at the appropriate changes to allow json-io to be used as a substitute for Jackson. Furthermore, there is an upcoming JsonCommandServlet that will give you a servlet that will receive JSON 'commands', process those, and return JSON output back to the browser (calling Javascript).
This version will support full graph serialization (cycle support) unlink the JSON2.stringify(). The November release is just of the JsonReader/JsonWriter. Likely in December / Jan timeframe the JsonCommandServlet will be released.
Regards,
John