When a new user ask a duplicate question, it most of the time ends up being closed as duplicate with a link to the original, usually with a comment saying "When you have earned enough reputation you'll be able to comment on other post etc.".
That's great for helping him finding an answer but what if the answers are out of date ? Or does not answer the question in a satisfying manner ? Then he/she find himself stuck without reputation and no way of getting an answer to his/her question.
I wonder why wouldn't we allow users that does not have sufficient reputation to post comment on the original question that made their question being closed as duplicate. That way they still can't comment on every posts (and still require 50 reputations before becoming more active on the site), but they can at least get an answer which is in my opinion the goal of Arqade. Even better they could poke an old and inactive question with out of date answers so the answerer can update their post, resulting in a better quality content on Arqade.
Regarding the abuse : Post a voluntary duplicate in order to be able to comment on the question.
I already had given it a tought : Even though that's an abuse resulting from this potential feature. I think it's a lot of work to go through just to be able to put comment on 1 question. If I wanted to make Arqade users/moderator/expert etc. lose time, I could simply open a lot of question (with multiple account), I could edit post forcing people to review them etc. I think there are many way that we can abuse Arqade system just to make people lose their time but this one seems like a lot of work (Askign a question > waiting for it to be closed > I can finally comment on 1 question). Gaining 50 reputation seems a lot faster, this become even more relevant if you allow only 1 comment (for example on the accepted answer).