Do not use non-core systemd

Yes, the systemd-networkd configuration system is fantastic, and as you say the fact that it uses the same configuration mechanisms as the rest of the systemd means you get drop-in support for free, and in my mind that's worth the price of admission. The ability for a tool like Ansible to manage an underlying network interface with VLANs on top of it in separate (but additive) configuration files is really powerful.