It's hard to compare something as being the Hacker News of "X", but one forum that has been filled with pretty solid discussion is https://bitcointalk.org/. Contrary to its name it also holds discussions on other crypto topics in the 'Altcoin Discussion' section.
All the cool kids, moon boys and the crypto hype squads are screaming in here: [0]
If you hate cryptocurrencies or crypto maximalists, beware.