I was in the midst of writing a snarky reply and then realized my actual issue with Kafka is that people reach for it way too often and use it in ways that don't really make sense.

Kind of like how people use docker for evrything, when what you really should be doing is learn how to package software.

What's wrong with kafka or what WILL BE wrong with kafka?

Nothing inherently wrong with the core product IMHO. The issue is more with Confluent, who have been constantly swinging from hot buzzword to hot buzzword for the last few years in search of growth. Confluent cloud is very expensive, and you still have to deal with a surprising amount of scaling headaches. I have people I consider friends that work there, so I don't want to go too deep into their various missteps, but the Kafka ecosystem has been largely stagnant outside of getting rid of Zookeeper and simplifying operations/deployment. There have been some decent quality of life fixes, but the platform is very expensive, yet if you are really all-in on Kafka, you would be insane to not get support from Confluent- it can break in surprising ways.

So you are stuck with some really terrible tradeoffs- Go with Confluent Cloud, pay a fortune, and still likely have some issues to deal with. Or you could go with Confluent Platform, still have to pay people to operate it, while Confluent the company focuses most of their attention on Cloud and still charges you a fortune. Or you could just go completely OS and forgo anything Confluent and risk being really up the river when something inevitably breaks, or you have to learn the hard way that librdkafka has poor support for a lot of the shiny features discussed in the release notes.

Redpanda has surpassed them from a technical quality perspective, but Kafka has them beat on the ecosystem and the sheer inertia of moving from one platform to another. Kafka for example was built in a time of spinning rust hard disks, and expects to be run on general purpose compute nodes, where Redpanda will actually look at your hardware and optimize the number of threads its spawns for the box it is on- assuming it is going to be the only real app running there, which is true for anything but a toy deployment.

This is my experience from running platform teams and being head of messaging at multiple companies.

https://en.wikipedia.org/wiki/Enshittification is helpful if you arent aware of how late stage capitalism works