The first thing that came to mind is it would only be possible to do this for the original post because it would be nearly impossible to be able to calculate how many of the readers read each comment. Further if it was implemented it would have to be able to count one reader per username, or more specifically one reader per person that can vote. that way if lets say i were to read an article but come back multiple times to read different comments it would not skew the ratio.

As a side note to this we could also implement a ratio per username that would show (post read)/(post voted on) so we would be able to see which users participate in voting at all. This however is nowhere near as useful to those who post as the original ratio and could have many possible downsides that i'm not going to take the time to think about because it will probably not be considered, but it is a fun idea.