The first step in generating a packfile is understanding the packfile. So I've been writing a Winxed disassembler. It's pretty fully featured at this point. It's showing constants, annotations, and symbolic instructions. Despite my fears, it turned out that PCC wasn't all that difficult to deal with.
To let people keep up with what the disassembler is looking like, I'm posting sample output as a gist. You can see how it's evolved by checking out the revisions on the right. The disassembler itself is part of PACT. The plan is for it to disassemble to PACT nodes. The PACT repository is on github: https://github.com/parrot/PACT