Just to clarify: We have the ability to block domains. Doesn't work quite the same way as one would want an instance block, however. Have tested it out lol
That being said I do believe a proper instance block is in the works for kbin according to ernest.
That doesn't work. You can block it but the communities on that instance will still show up. I tried that already with that furry instance. lemmynsfw is still defederated though, so you won't see it on kbin anyway.