This is an idea for a mailcap for cpio to list the archive contents.
tar and unzip have similar for tar and zip files.

The "debian/cpio.mime" file below is installed by the rules.diff below
to /usr/lib/mime/packages/cpio and the mime-support package does the
rest.  With this it's then possible to "see" a cpio file,

    echo /usr/share/base-files/motd | cpio -o >/tmp/foo.cpio

    see /tmp/foo.cpio
    =>
    -rw-r--r--   1 root     root          286 May  6 22:45 /usr/share/base-files/motd
    1 block

(The filename cpio.mime is per debhelper dh_installmime, which is not
used now of course, but if it ever was then it would suit.)