I'd very much like to see this done, at least for questions with suggested duplicates.
Why do I want this? Well, the notice placed on questions closed as duplicates looks like this:
This question already has an answer here:
Link to duplicate question n+1 answers
The way I see it, if the closed question already has answers, there is, or at least should be, an implied "better" there. There's no point in closing a question with a great answer as a duplicate of one with merely a decent answer. In fact, doing so is actively counterproductive, since it directs visitors to the less well answered question.
Currently, if a question in the duplicate close vote review queue already has answers, the only way to see them is to open it in a new tab. To add insult to injury, the tabs showing the suggested duplicate questions do include their answers; it's only the answers to the question under review that can't be seen through the review interface.
Anyway, I was going to make a separate feature request for this, but I figure this one is close enough, so I'll just put a bounty on it to give it a bit more visibility.
Ps. Since the extra attention I was hoping for doesn't seem to have materialized, and since I can't award the bounty back to myself, does anybody want +200 rep as a Christmas present? Just post an answer... ;-)
Update: Stack Overflow Unofficial Patch v1.10 now contains a client-side implementation of this feature. It works by detecting the presence of un-displayed answers (based on the summary table) and loading them via AJAX instead. There's some kluginess involved in reformatting the answer wrapper elements to fit the review page format, but overall it seems to work nice and smoothly.
Here's a screenshot: