Idea for joinmastodon.org (those are dropdowns).
I thought about the instances.social wizard and tooter.today a lot. And I couldn't come up with any options better than interest and language. I don't think new people know what size of community they prefer, nor do they want to choose things like "untagged NSFW"
Here is a video demo, with bad data: https://webmshare.com/6jbez
Actually getting the categorization data from somewhere is gonna be a challenge.
Server run by the main developers of the project It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!