We really cannot answer questions that start with "when?"
There has been significant progress made recently on getting Rockbox to work on the 80GB iPod, but there is more work to do. Since that work is being done by volunteers working in their spare time, it is difficult to say how long it may take or when it will get done. Also, to some extent, progress depends on being able to make breakthroughs with respect to undocumented hardware, and it is impossible to predict when those breakthroughs will happen.
If you want to follow the progress on the 80GB, you can read through this thread:
http://forums.rockbox.org/index.php?topic=7738.0(However, please don't post in that thread, as discussion there is limited to discussion relating to development, and posts asking about the status are strongly discouraged.)
You can also follow the progress of the work being done by LinusN and others in this Flyspray patch:
http://www.rockbox.org/tracker/task/6549