Erik Christiansen:
Gene, ifconfig is SysV flavoured, so not favoured on the Systemd journey, AIUI.
van Smoorenburg init and systemd actually have nothing whatsoever to do with it. ifconfig uses one Linux API for sending information to and from the kernel, ip uses a different Linux API. Ironically, the net-tools package is completely Linux-specific *anyway*, so the usual argument that ifconfig couldn't be changed to use the other API, because it has to remain portable, does not hold any water.
That said, one of the things that in practice ifconfig falls down on in real world use, where most of the use cases are fairly conventional and humdrum, is in IPV6 support:
root # ifconfig lo inet6 ::1 Don't know how to set addresses for family 10. root #
This is actually a fairly trivial oversight in a case statement in the code, rather than a fundamental design or implementation problem, though. It doesn't even need the other API.