You: Apple rebadges Dell
Me: Apple sources from a supplier, and typically has an exclusive for a year, after which Dell begins sourcing from the same supplier.
If they release a high-ppi iMac, it's either going to be QFHD, or some new arithmetic magic needs to be invented to make up for scaling NPOT. While the latter is not impossible, I don't think it's going to ever happen, or that it even needs to happen. That said, I don't think we'll see a QFHD iMac this year, and will be shocked if Apple pulls it off. Late 2013 is probably when we'll see large high-ppi displays in the consumer space.