See https://github.com/canonical/netplan/pull/456#discussion_r1569065581
The way the netplan + networkd integration is designed requires all the network devices (wlan0 in particular) to exist at /sbin/init time - otherwise, the netplan generator disables `systemd-networkd-wait-online.service` which also causes `network-online.target` to be reached early. In particular, this breaks any network FS mounts on boot.
Of note, I tried logging in to file the bug via the dev contribution platform, but it looks I'm blocked from JIRA access, so am filing it here instead.