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.
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[ 2.6 ms ] story [ 14.5 ms ] threadIf you hate cryptocurrencies or crypto maximalists, beware.
[0] https://cryptopanic.com