Then riddle me this, Giskard. If any manufacturer on the planet is building an IPS monitor at the kind of low price-point you have in mind, how come we haven't heard of it? Apple isn't going to make a display itself, it's going to have to go to some supplier. and no company in the world has demonstrated the capacity at making an inexpensive iPS monitor (Apple asking $3500 for the Sharp model they offer as a MacPro add-on, although you can buy the same unit from Amazon for $3000). If a 27-in 4k iMac is going to be announced in less than two weeks, presumably it will be on the market no later than Dec. 1, in order to take advantage of the seasonal buying surge, and you are asking Apple to make a technological leap forward over the next couple of months which is in all probability impossible. And if it were possible, wouldn't the rumor mills be working overtime already?
On the other hand, if Apple sticks to TN technology it can probably bring in an iMac at a price not dramatically higher than the present model. A highly likely supplier would be Samsung, whose U28D590D, a well-received TN monitor has been on the market since June. Its current list price of $600 (which I believe was originally $700). If Apple made it worth their while, it would presumably be no great feat for Samsung to produce a revised version at 27" (if Apple went to a 28" iMac they'd have to do a lot of factory retooling to manufacture larger cases and a cascading series of resulting design changes, which might be quite expensive).
So, given the current industrial realities, I think we come down to one of two possible alternatives: a super-high-end IPS model at a price point, as I originally said, north of five grand, sold in addition the current model, or b.) a TN replacement iMac sold at essentially the same price as the current one.
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This might be a straw in the wind: http://www.cnet.com/news/intel-to-deliver-cheaper-4k-monitors-thanks-to-samsung-partnership/
I have to agree with this as well, unfortunately, especially taking into account that Apple cannot leverage the kind of volume purchase effect that they can with iDevice components. They just don't sell enough Macs, let alone iMacs, to bully the supply chain like they can with thier mobile devices.