I made a Magazine called Photobiomodulation (https://kbin.social/m/photobiomodulation/) for the discussion of this topic on the Fediverse. I've left Reddit behind, and am recreating this community here.
My advice would be to not wait for someone else to create communities would like to see, but create them yourself and just start posting. If you are not interested in moderating I’m sure you will be able to find someone else to take over.
You can post them in !newcommunities to get some attention, but like minded people will find you.
What niche communities are you all looking to find/found here on lemmy?
I would love to find someplace to talk about roadtripping, comparing routes and whatnot.