http://phoronix.com/scan.php?page=news_item&px=Ubuntu-Netplan-YAML-Network
With netplan there are central /etc/netplan/*.yaml network config files for *all* Ubuntu — Snappy, Server, Client, MaaS, cloud-init. All installers only generate such a file, no /etc/network/interfaces any more.
This then gives us the flexibility to dynamically select or switch between different backends — for example, there is demand for moving away from ifupdown towards networkd, and some environments might prefer NetworkManager for everything.
netplan translates the YAML config to the backend specific configuration formats on boot, but all these are only written to /run — i. e. they are ephemeral and not considered primary configuration files in /etc.