There's no reason you couldn't do it right now with the existing infrastructure on HN. It wouldn't be as fancy (e.g. the AMA subject's comments highlighted) but it would be just as functional, down to the ordering of the questions in the comments.
The default sort order is either best or top scoring which will rank comment order by vote score, I generally sort by "old" (oldest first; chronological order.
If you have an account you can alter your default sort preference.