Context is important. The replied-to comment starts off, "While this particular implementation doesn't track individuals, couldn't your trivially start tracking individuals by[...]"
An acceptable response, then (to both you and the original commenter), follows: "While some particular browser version doesn't currently protect individuals from that proposed form of tracking, any browser vendor could trivially start thwarting that form of tracking by exploiting the latitude afforded to UAs by the semantics of these headers." And that's the form that the previous comment takes and how it should be understood. The fact that "users go to the web with the browser they've been given [i.e., today, and which isn't providing this sort of tracking protection]" doesn't change anything; we are explicitly talking about steps that each side _can_ take in the arms race related to the subject of this discussion...
An acceptable response, then (to both you and the original commenter), follows: "While some particular browser version doesn't currently protect individuals from that proposed form of tracking, any browser vendor could trivially start thwarting that form of tracking by exploiting the latitude afforded to UAs by the semantics of these headers." And that's the form that the previous comment takes and how it should be understood. The fact that "users go to the web with the browser they've been given [i.e., today, and which isn't providing this sort of tracking protection]" doesn't change anything; we are explicitly talking about steps that each side _can_ take in the arms race related to the subject of this discussion...