What the heck is Apple waiting for? Retain the present shape, or (preferably) make the iMac slightly thicker. Then offer an iMac 27'' with the newest line of Intel CPUs and Nvidia GPUs (including 1070M and 1080M). Get your act together, Apple. Focus a little less on politically correct virtue signalling and empty promises about "great products", and just simply deliver some new desktop products.
PS: If the new iMac line is as outrageously priced as the latest MBPs, then I'll stick to my late 2012 iMac or buy a PC, thank you very much. To demand that kind of prices for your products, when you as a company are paying downwards of 0.005% taxes in Europe, and hoarding hundreds of billion dollars of cash in tax havens is simply ridiculous.