Speaking as a bystander who mainly reads blogs, my perception of Kafka is that it's marketing (for lack of a better term) has successfully positioned it with "we can keep your arbitrarily large logs" and "they are pretty durable, consumers can revisit them if they fall behind".

This offers a nice distinction from MQ-ish systems, where the emphasis seems to be on a different set of benefits like "we can handle complex centralized distribution logic for you" and "we help manage your synchronous calls".

Does that seem accurate in terms of how Kafka is evolving its future niche? Personally, I'm interested in optimistic-locking when adding to a log.