With discourse, I think there will be more noise and a lot of time will be wasted scrolling through unnecessary replies. What's good about the thread-like nature of HN/Reddit is that you'll have proper context and the rating system does its job so everyone's time won't be wasted.
Questions can be answered here and on Reddit too. I think Reddit can be sometimes more helpful than HN when it comes to answering 'easy' questions so I would go there if you have any simple questions.
[1]: https://www.reddit.com/r/MachineLearning/comments/63f3uk/r_w...
These articles on distill I believe could greatly benefit from this. Let the community help distill.
And if there is a question that requires more control, like math formatting, etc. I would actually suggest posting to cross validated[1] and then linking it here.