The very definition of over-engineered. This is just event-sourcing turned into a marketing article for Kafka.
It doesn't really matter what the "source of truth" system is, although Kafka doesn't seem quite as mature/stable enough for that. With such little data, they can push into a nice graph database instead, run it entirely in memory and meet 10x any demand they'll ever see along with all the query types they'll need. Add in an elasticsearch cluster on the side and problem solved.
Any database can serve as a log replay, as long as you save all the versions then it's just called a query.
It doesn't really matter what the "source of truth" system is, although Kafka doesn't seem quite as mature/stable enough for that. With such little data, they can push into a nice graph database instead, run it entirely in memory and meet 10x any demand they'll ever see along with all the query types they'll need. Add in an elasticsearch cluster on the side and problem solved.
Any database can serve as a log replay, as long as you save all the versions then it's just called a query.