I can migrate it to readme.gentoo.eclass if you want:
mate-file-archiver is a frontend for several archiving utilities. If you want a
particular achive format supported install the relevant package.
7-zip : emerge app-arch/p7zip
ace : emerge app-arch/unace
arj : emerge app-arch/arj
cpio : emerge app-arch/cpio
deb : emerge app-arch/dpkg
iso : emerge app-cdr/cdrtools
jar,zip : emerge app-arch/zip or emerge app-arch/unzip
lha : emerge app-arch/lha
lzma : emerge app-arch/xz-utils
lzop : emerge app-arch/lzop
rar : emerge app-arch/unrar
rpm : emerge app-arch/rpm
unstuff : emerge app-arch/stuffit
zoo : emerge app-arch/zoo
mate 1.6 was obsoleted and removed from the tree.
With this app-arch/mate-file-archiver will also be removed (not part of mate 1.8 any more)
As this does not block any further process, I just close as obsolete.