Comment # 10 on bug 900505 from pgnd _

Although neither

   
http://www.freedesktop.org/software/systemd/man/systemd-networkd.service.html 

nor

    http://www.freedesktop.org/software/systemd/man/systemd.network.html

so explicitly state, additional comment at

    https://wiki.archlinux.org/index.php/systemd-networkd

suggests that 

    " ...
    This service (systemd-networkd) can run alongside your usual network
management tool
    ... "

As, with systemd-networkd,

    " ...
    Networks are configured in .network files, see systemd.network(5), and
virtual network devices are configured in .netdev files,
    ... "

Given that

    " ...
    It detects and configures network devices as they appear,
    ..."

it seems reasonable, though currently untested here, that if systemd-networkd
were, instead, ENabled (or, technically, not DISabled), it could coexist
peacefully with NetworkManager/Wicked's "other" requirements, particularly if
no .network or .netdev files were populated by default.

And the aformentioned 'detection' might (?) be the mechainsm by which to ensure
upstream systemd compatibility/completeness of network* unit ordering.