Earlier quoted context omitted.
If people were to pick one reason HN has 'gone downhill', disrespectful comment replies would top the list. A controversial feature request- when a new account reaches a negative karma level within a certain period, HN will display all other usernames associated with the IP address of the throwaway.
I'd suggest something different. Reduce the value of throwaway logins by making it impossible to comment for, say, 40 days. We can then modulate the quarantine period according to the level of hostility present on the site. Of coursesmart, flagging and hellbanning remains as usual.
I like the idea of an incubation period, but I've seen valuable comments posted from new accounts- I bet a ton of people lurk for months before seeing a thread they feel they can make a valuable contribution to.