+1 for martial arts in general. Depending on the art it might not be niche (I'm sure karate and taekwondo are too big for that). But things like HEMA, iaido, eskrima, all kinds of archery, ... are great fun and typically come with smallish & fun communities.

Edit: before you think these arts are immune to tech, I once had a student who built a (truly awful) sword fighting "robot" to help train deflecting strikes. Not quite up to par with Dune's robot swordmasters.