FYI, I enclose the init of Debian 8.0.0. It makes heavy use of other scripts, and the large initrd.img size is mostly because of most of std Unix /bin, /sbin and quite a bit of /usr/lib is packed into it. While e.g. Knoppix has traditionally been based on lightweight busybox. But this ought to make modifications simpler, actually. Because we may assume everything works as expected. (Which is not always true for busybox versions of, say, mount.)
Seems to me that it should not be extremely dfficult to Knoppify this a bit?