CHDK ports when someone with the required skills has the camera and is willing to invest the time to make it happen. There is no schedule, and there's not much a non-developer can do to make it happen.
Generally, when a port is started, there will be a thread for it in the development section, and the wiki page for that camera will be updated to link to it. The page for the SD880 is
http://chdk.wikia.com/wiki/IXUS870IS and there doesn't appear to be anyone working on it.
I don't expect digic IV to be much of an obstacle, I've looked at quite a bit for the sd990 port and so far it's all pretty much the same. The 12 bit sensor (vs 10 bit on older cams) may delay raw support, but sharky is already making good progress on that with the sd770 port.
