Yes, the core folks in Redis now have outlined a plan for moving towards multi-threaded awhile ago. It's honestly not made a lot of progress because raw performance matters a lot less than is argued here. As was succinctly mentioned by antirez already, Redis scales comfortably to 100s of millions of QPS with cluster mode. So, it's really building a lot of custom functionality to support better vertical scaling. Which is useful, especially when the vertical scaling keeps you on a single process.

The conversation happened here, https://github.com/redis/redis/issues/8340, and it's not like the most pressing issue for the project. It's also not as complex as what was implemented for dragonfly, which basically has native support from the ground up for concurrent programming during command execution. It would be hard to do in C as well.