>Sure, relatively modern (RFC5424) syslog protocol has structured data too, but in my experience most software had never bothered to use it. So, forcing a switch through introducing another protocol that has structured data baked-in isn't a too terrible idea.

I agree. There is a strong need for common interface(s), and that's a strong part of the motivation behind Fluentd/Kafka/etc. www.fluentd.org/blog/unified-logging-layer