Yes. I am not sure that I will get started full before the end of February, but I intend to contribute to
1. Java 1.1.8 version 2. keep-with 3. Encryption
Keeping jdk1.1 support is a hinderance to the development of FOP and as such has been dropped. Since the code is available you can alter for you own uses but there will be problems.
Encryption is the best place to start to get into FOP. You can concentrate on a smaller section of the code and get to know some of the internals of FOP. It should be fairly straight forward in terms of where to put the code and how to integrate with other code. The feature itself may not be easy but the is Adobes fault. Almost all the pdf code is in org.apache.fop.pdf.* (should be all of it but alas). If you need help, just yell.
The keep-with is about the redesign. Once you know something about the internals of FOP you will need to know all about - xsl:fo and the layout process.
All of those are things that I potentially need.