I think the key part of the UX there is the instant pop-up visibility of the linked comment when you hover over it. Navigating between comments seems like the

I think the key part of the UX there is the instant pop-up visibility of the linked comment when you hover over it. Navigating between comments seems like the biggest barrier for most users, where even the extra couple seconds to find out what the person is replying to may be enough to deter someone's interest. And if you accidentally click the wrong place or hit back too many times, it's easy to lose your place.