I am working on an (external) application which will indirectly make this possible for HN threads (I plan on doing a "Show HN" to demonstrate it).<p>However, in the case of a feature directly within the HN interface to collapse all non-top level comments, I think the only option right now would be to write JS to fire click events on the DOM to collapse non-top level comments, and inject it via the console or an extension while on HN.