I agree they won't give it away, but their price structure basically always remains the same, only the hardware you get for your money changes, looking all the back to the 1GB that was standard in my 2007 iMac.
Price points remaining static is a key Apple marketing feature along with base model, better, and best SKUs. They don't bump big things like storage or RAM that often and when they do they generally keep the price static which represents a massive step-up in value.
However, to get Fusion drive into more SKUs Apple crippled the amount of SSD you get from 128Gb to 24Gb in 2015*. So unless they have cut a sweet deal with Intel to get Coffee Lake chips cheaply, or AMD hand over cheaper 500X GPUs (especially since the 500X seems to be not much of an upgrade on the 2017 500 series) I find it unlikely that Apple would hand over 16Gb of RAM for free.
There's room for manoeuvre by Apple to make changes to list price but bear in mind if they decide that the Coffee Lake iMacs are going to have T2 co-processors (as seen in the iMac Pro and T1 in the MacBook Pro) the price will only be going up. That's when you can package the increase with higher standard RAM and extra cores.
If the iMac range is going further upmarket thanks to more standard RAM, a T2 CPU, and the appearance of the iMac Pro, this could help with an upgraded Mac Mini (Pro) which might be better equipped to fill the (larger) gap. They don't even need to make too many SKUs - just have one fully loaded for $2k (incorporating the T2, 16Gb RAM, 512Gb SSD) and ready to buy off the shelf with BTO extras from Apple.
* One little known fact with the 2014 Mini is that the 1Tb Fusion drive on the top SKU predates the smackdown on the SSD portion of 1Tb drives in 2015 and later iMacs. A 1Tb Fusion drive on the Mini has 128Gb SSD, whereas the 1Tb Fusion on the 2015 and 2017 iMac has just 24Gb SSD.
This represents one benefit of Apple never changing the 2014 spec since October 2014.
We're only a 8 days away from WWDC, I guess we'll soon know the truth of the matter.