On my Archlinux rpi2 machine with systemd 218-2, I had something like
I like the flexibility because I may move between eth0 & wlan0.
But that doesn't hit the network-online.target since IIUC since other devices are in the configuring state:
What I expected to happen is that given any routable network interface, network-online.target gets hit by systemd-networkd-wait-online.service since the network *is* online.
Or http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget/ should be updated to make this expressly clear. The workaround is to explicitly name wlan0 and lose the flexibility of plugging in a ethernet cable alternatively IIUC.
Please use --any option.