P.S. I'll also address threading and persistence.
Redis is exactly the kind of software that gives me joy. Aesthetically and intellectually. Its pieces are orthogonal -- a word you used in your blog post. The code is small, tight, and well designed. It invites you to think more creatively. The lolwut command was also a very good innovation!
> Let me show you an example. You have a Redis instance and you plan to use the instance to do a new thing: delayed jobs processing. You get a library from the internet, and it looks to work well. Now why on the earth such library, that you don’t know line by line, should be able to call “FLUSHALL” and flush away your database instantly? Maybe the library test will have such command inside and you realize it when it’s too late. Or maybe you just hired a junior developer that is keeping calling “KEYS *” on the Redis instance, while your company Redis policy is “No KEYS command”.
Without ACLs we need to rely on command renaming or completely isolating databases to guard against errors. ACLs sound complicated but they're actually a solid user experience improvement.