My impression is dang makes a lot of behind the scenes changes, but few public changes. As such, they’re hard to notice and really become a topic. There a lot of features HN has that most users don’t know about and/or use too.

This may be true. But I think the greater value of HN is in fact the community: the set of people who use it and the norms that have emerged, more than the features. I think encouraging more "slow" conversation would improve this community, and it would not be too risky to test out more default comments notification.

I use HN replies (and RSS)... but very few others do, so the the change of getting a reply to this comment is low, even though I got here within a day.

Hi! I don't use HN replies, but I do go back and check my less-than-day-old comments.

When I say a system, I'm including everything, including the community. It's not any one part of HN, it's the way all the parts interact. Seemingly small changes can have a dramatic impact on the way the system operates, which includes the community. Suddenly different voices become amplified while others feel marginalized, and it's hard to predict if that will be a good outcome.

I'm not saying that it would for sure be a problem, but I sympathize with dang wanting to be very careful before introducing something like that.

Nice, thanks for the reply! I agree - I'm also very sympathetic to that. In this case, I think it is an example of a feature worth experimenting with, even if slowly. I would love to have more slow threads like this one.