This page describes the effort toward a JDOM 2.0 and provides an entry point for all the information you need on JDOM2. Skip to the end of this page to get the status of JDOM 2.0 and a list of JDOM 2.0 related pages.
The purpose of JDOM 2.0 is to make use of features introduced in Java 5, such as generics (note JDOM officially supports Java6 and up though - see the Java Dependencies/Versions page). Unfortunately the generics changes will break binary backward compatibility so we're moving to a new version as well as a new package name: org.jdom2. People who want to use the JDOM 1.1.x branch can continue to do so, but people who want the modern features can use JDOM 2.0. The same program can even mix and match. Yes there's downsides (http://markmail.org/message/avsyrgfii7z3u6m5) but it's probably worth it.
How much backward compatibility will we break? Only what's necessary. We may maintain source code compatibility so all a programmer will need to do is update their package imports and recompile their project. But if we decide as a group that some changes are so advantageous they're worth requiring code edits, we'll do it.
We'll do the work on GitHub because it simplifies the task of doing experimental branches. I expect a lot of discussion about whether a certain change is worthwhile or not, and GitHub makes it easy to discuss code not just ideas. The JDOM mailing lists will host the discussion. You can also watch for updates on Twitter from @jdomproject and @jdomcommits.
Possible JDOM 2.0 improvements (see JDOM2 Features for more details):
People who have volunteered to be heavily involved in the project:
JDOM 2.0 is ready to release. Easter 2012.
There are currently only smallish features that are outstanding on JDOM 2.0. The big features have been completed. See the issue tracker for what's outstanding.
JDOM 2.0 information is a little scattered in the github site. These wiki pages are used for tracking some of the major features and non-javadoc documentation. The GitHub Downloads page is used to provide development snapshot downloads. The Github web-pages are used to supply HTML-based content, including the JavaDoc, Performance, JUnit, and Coverage reports.
Here are the references to the major JDOM 2.0 web-based resources. Some of these are duplicated in the 'sidebar' on all the GitHub JDOM wiki pages: