The roadmap is just what I'm thinking, but it might go different if someone decides to contribute something.
Target for 1.0.
After 1.0
You can download the latest source from sourceforge.
To compile, you need to set the following preferences:
'Plug-In Development: Java Build Path Control: Use classpath containers' to true
'Plug-In Development: Target Platform' select "this application" and enable all plugins.
Most of the code is well-documented in javadoc. I try to cc every answer to a coding question to pydev-code, so you can look there for hints too. That's it. If you have not developed Eclipse plugins before, I recommend reading the online documentation and trying out a sample plugin. Doing some prep work before jumping in will really pay off.
Then, it is all up to you.