Hashtags aren’t a thing here and they have their downsides, but they would definitely make trending topics and memes easier to detect, categorize and surface to users. 

I have put all casts through topic detection ML and its not that easy to find the signal in the noise. It might also just be my lack of ML skills

NLP is the hardest part of the stack. Probably not your lack of skills. Categorising untagged content is brutal.

They aren't used on Twitter that much (compared to 5-10 years ago), and promote gaming.

imo something that was floated (perhaps by @dwr , can't recall off the top of my head) as far as ______caster doing something to organize via topic/community is way better and will dis-incentivize bad behaviour.

Searchcaster