My guess is that once ( IF ) the new iMacs are launched, Apple will replace all the Apple shop iMacs with the new ones, that is if they are classed as a replacement and not a High spec model and existing range is kept.
Therefore all the shop models will be returned to factory to be refurbished / polished / reformatted and then they will be put onto the Apple Refurb shop over the following months, don't think we will see a big price drop, Apple will continue to manage the supply chain to keep prices about 20% lower than RRP.
The main difference I think we will see is that the model will change to being late 2013 / early 2014 rather than early 2013.
Just a view
Taff