so far found this:

echo "working" | systemd-cat -t keepalived -p warning
echo "missinginaction" | systemd-cat -t keepalived -p info

changed

[email protected]:~# cat /etc/rsyslog.d/vyos-rsyslog.conf
[..]
*.debug :omfile:$global

[email protected]:~# grep ^# /etc/systemd/journald.conf  -v

[Journal]
ForwardToSyslog=yes
MaxLevelStore=debug
MaxLevelSyslog=debug

MaxLevelStore because of bug 1370195 but should already be Debug by default. Might not be necessary.

to get it working. But then I thought, isn't this

set system syslog global facility all level notice

fault? ie. PEBCAK

Maybe it merits the larger question on howto migrate this away from rsyslog (if at all) and create sub-tasks.

It's not really a bug, the log level is per default set not to log everything, like @EwaldvanGeffen stated above.
'set system syslog global facility all level all' will log everything, embedded users with flash drives will hate us for this if we change it :).
In my opinion, if someone needs to debug anything, he/she can just set the global logging or even to a particular file for debugging.
Otherwise, we can just change the section in the default config to have logging anything enabled per default, which increases the risk for losing information due to disk space limitation for /var/log as well as the quicker rotation (only 5 files are being stored per default).

I'm going to verify @dmbaturin patch to set level to info. Additionally we could also use immark, which leave a 'heartbeat' marker in the logfiles, so one can verify logging at least works. It would be visible to remote logging as well.