As the link-sync patch was removed from the qmail ebuilds, why not add support for the syncdir library, which seems to be approved of. It could be added with a useflag, and all it takes is to add two dependencies: "x86? ( dev-libs/syncdir ) sparc? ( dev-libs/syncdir)" (syncdir is only keyworded for x86 and sparc) and an "append-ldflags -lsyncdir".
Maybe in -r17
We won't add more stuff to mail-mta/qmail. If you need special patches, use mail-mta/netqmail with QMAIL_PATCH_DIR.