The sys-apps/xinetd ebuild files reference https://www.xinetd.org and https://github.com/xinetd-org/xinetd as upstream. The web site has been offline for a long time and appears dead. The git hasn't been active in a long time and the Debian xinetd maintainer posted an issue there 4 months ago: https://github.com/xinetd-org/xinetd/issues/30 saying that OpenSUSE has a git here: https://github.com/openSUSE/xinetd and OpenSUSE and Debian are now using that as their upstream. That new git is active and the latest release "2.3.15.3" is slightly different than Gentoo's latest "xinetd-2.3.15-r3". Should Gentoo switch to the new upstream?
They even did a few minor releases past 2.3.15.
2.3.15.3 is in the tree.