Not really. We use two text based formats for logging: BSD syslog, and systemd's structured logging (which is basically an env block, i.e. a key-value set, with some tweaks). Programs generate text logs, journald reads text logs hence. Programs that read from the journal get the text-based key/value stuff back, usually.

(Yes, we then store the structure log data on disk in a binary format. Lookup indexes are just nasty in text based formats).

Hence, not sure what the Journal has to do with Varlink, but any IPC that the journal does is text-based, and very nicely strace'able in fact, I do that all the time.

[Maybe, when trying to be a smartass, try to be "smart", and not just an "ass"?]