The GPU update was the only reason I was waiting. From Apples point of view, what's the point of updating now if the main additions are just the GPU... with USB 3 and IB as very minor upgrades. If they don't have a redesign to go along with that there is not much motivation to release a new machine from my point of view. The 7970m is still going to be a great card 6 months from now so they don't really have a reason to rush out a release if they are working on a redesign.
With the new Apple TV rumors that have been popping up and past rumors of it being built into the iMac I could see them pushing release of a new machine to really wow the market. People want retina? That has been estimated as being year(s) out... another 9-12 months they could release a redesigned iMac that includes Apple TV, a retina display and whatever new processor/graphics card is available. That would also be around the same timeframe where HDD constraints should be minimized.
First- Why would Apple not release a 2012 imac
Second - why would they wait 6+ months, ruins calling it a 2012,year model
Third - retina for a 27" imac is not for 2012 + $$ for that and tv function are way too high when buying a computer
Fourth- to do so,Apple would loose a new product / sales margin
Fifth- all imac parts are in, competition is shipping Ivy now. Cant wait much longer + each revision does not have to be major design
Sixth- some people will still complain about a refresh while others love it
Seventh- wwdc is the latest & for sure well know news before then