You can block pretty much anything on Amethyst, and also nostr is in its very early infancy.

As more people join, relay runners will want to attract different kinds of crowds and it will become easier to identify relays that permit nsfw content and avoid them. Relay management will probably be built in in more seamless ways so you can hit a button and disconnect from all nsfw tolerant relays.

If you don't want to give it time to mature and use these features in the future when someone else builds it, build it yourself! Open protocol, free country. I hope you do, I'd like to see this. I'm just also good to wait on it, but I'm sure it will come.