Well, with some apologies for the delay, I'm finally delivering something for cpio-mode. A tarball is attached.
Right now the only format that's supported is newc. The others will be coming, but the reality is that the formats are the easy part. Similarly, only file and directory extractions work at the moment.
To use this
1. Read a newc format cpio archive.
2. M-x cpio-mode in that buffer. (This should get you a dired-like buffer.)
3. Do basic dired-like things in this buffer.
Many commands have mappings, but most don't have implementations. If you try to use a command that's not implemented, then an error to that effect is signaled. (dired turned out to be bigger than I expected.)
The long-term intent is for the archive to be entirely editable. You should be able to edit entry contents, save them into the archive buffer, touch entries, change modes, owners and groups, add and delete entries, etc. Archive detection is also a goal, so you would get cpio-mode for free with the appropriate find-file hook.
All comments are welcome.