This is fetishizing complexity for no reason. Makes for an interesting blog post, but if any company told me they were doing this I would run the other direction immediately.
Democratisation of complex machinery like the raft and consensus algorithms, schedulers, append logs, query optimisers and so on is a superb thing. It is something that has only been possible in the last 3/4 years and would have been devilishly difficult before then without significant upfront work.
Fetishising complexity might be a bit strong here. Seeing more posts like this is a good thing.
At the same time, OP is right: a business doing this is making poor engineering decisions.
But no need to jump to conclusions. I've seen plenty of bs fragile ducktape databases. Some of them exist because because someone wanted to hand-roll everything. And some exist because they were afraid to invent anything and ended up hacking together a bunch of garbage MySQL nodes. Because they didn't want "reinvent the wheel".
Specifics matter!
I also agree that the open source tech used in this solution is very powerful and it is great we are at a point where a solution like this could exist. I love avro schema registries and kafka just as much as the next guy.
Just from a hand wavy aesthetic perspective I like protobufs but I'd like to get a clear picture.
Projects like this are how we get solutions that blow existing stuff out of the water. Although a lot just end up being fun projects that amount to nothing but an entertaining blog article.
What's extra cool about this for me is how it illustrates to me how far open source components that build on the Apache Kafka ecosystem have come, to the degree that each fairly complex component of relational databases that expose a full RDBMS system from the basic building block of a log have been fully developed (to some production capacity) in the Kafka ecosystem. That's amazing! What does this mean?
It means that you could theoretically (please don't hurt me) implement a relational DB backed by a twitter DB log, or a blockchain, or any other event log that you can't necessarily use traditionally as a WAL. It also introduces a lot of really interesting possibilities for data integration. Definitely has my mind reeling a bit.
Do you run away from microservices too?