Feature request: When a question is closed as a duplicate (or merged into another), the author of that question should be able to comment on the parent question and its answers, irrespective of reputation.
Primary reason: low rep users are probably more likely to ask questions that have already been asked before and also more likely to not have the skills necessary to adapt the answers to the parent to their situation, the latter is needed since even if the questions are duplicates within the required epsilon, the answers to the parent might not be quite what the new poster is looking for and might need a little tweaking.
Secondary reason: having a question closed as a duplicate is not a bad thing, but this consequence (of not being able to comment) can mean that the user doesn't get the help that they need and which the community could very easily give. So it would be a more welcoming gesture to enable them to comment on the parent.
(I accept that this might be impractical - it would mean that parent questions needed to know their children.)