For real life reasons, I don't know when I will look at CHDK code again.
However, I haven't contributed to the port.
So far I have just been trying out some of the work Mariush posted, I set up my own build environment, and added some to the wiki.
So I guess a good checkpoint would be to look up the code that Mariush posted, hack around, post your findings, and ask questions here, that neither the wiki nor searching in this forum answers. I think people got rather far, as in cracking the shell of the nut. CHDK starts booting, and I think you can even make it do stuff. There is still lot of work left though, in mapping the reminding calls and possibly the hardware (MMIO) addresses.
Good luck!