kdeutils-meta has an optional dependency on various rar unpacking tools with the rar useflag: rar? ( || ( app-arch/rar app-arch/unrar app-arch/unar ) ) I believe this is obsolete. ark uses libarchive by default and can unpack rar files (including the latest format rar v5) with that. So unrar or unar aren't necessary to have rar unpacking support. (Only for creating rar files app-arch/rar would be needed, but unrar/unar wouldn't help.)
Sorry, I was wrong on this. I tested with actual unrar installed and thought it worked through libarchive. It turns out the libarchive plugin doesn't support rar. There was an upstream bug which was closed as wontfix: https://bugs.kde.org/show_bug.cgi?id=350054 This has been a couple of years ago, so re-discussing this with upstream may make sense, but in any case there's nothing for gentoo to do right now.
