Basically Kafka provides what NSQ is lacking:
Messages are durable (across nodes, not just persisted to the filesystem). Messages are delivered in-order (for a partition). Consumers know all partitions of a topic from startup, it's not eventually consistent.
NSQ has been great honestly, it was just designed with different use cases in mind.
NSQ is my go-to queue whenever I'm working on any kind of service, even more so when that service might be standalone. Consider deploying a service on an isolated box which frequently pushes data into the cloud. Connectivity to the cloud might be intermittent, so you just store every work item to the locally running nsq and you're protected against network outages as well as your data-producing process crashing. Since NSQ is so easy to spin up and easy to interact with (Publish works via plain HTTP), it's not a lot of overhead to add it to your process.
Re: msq: Looks like segment are using kafka these days despite the praise for nsq in this dated article.
The real allure was the guarantee that only one subscriber would get a request much like a traditional load balancer. The performance was an added benefit.
When we put it together a few years ago the cloistering wasn't very mature and the streaming version with persistence wasn't completed. Would look into this over kafka if only for the simplicity in management and track record of go for performance and reliability.