launchd (OS X) and SMF (solaris) weren't portable, either.
By the way, when was the last time a BSD operating system cared about making their init system portable to Linux?
I'm not sure why systemd not being portable to other operating systems is suddenly a big deal.
To support systemd, the number of configs you provide will go from maybe 4 to 5, not from 1 to 2! And, looking at the examples provided by ArchLinux, the systemd services look as if they are a lot less boiler-plate than the typical debian init-script.
https://wiki.archlinux.org/index.php/Systemd/Services (e.g. dropbear is very simple)
Because software being written that has systemd as a dependency will be Linux only software.
And this is news, and suddenly it's systemd's fault?
If you hate Linux-only software, software that depends on systemd is the last of your problems. Software that depends on glibc and the Linux kernel are probable the main offenders.