iFixit's teardown of the 5K iMac in 2014 showed that it was manufactured by LG. However, this is "just" the panel, which would presumably be at a much lower cost to Apple. When I tested out some 4k monitors before settling on the iMac I was surprisingly pleased with some of the 4K VA panels out there now, so long as you don't need wide viewing angles. Too bad the scaling on 4K is so taxing to the GPU for the resolutions I use.
<< LM270QQ1-SDC1 (Alias: LM270QQ1 (SD)(C1)) is a 27.0" diagonal Oxide TFT-LCD display panel product from LG Display Co., Ltd. (hereafter called LG Display), with an integral WLED backlight system, without touch screen. It features an operating temperature range of 0 ~ 50°C , a storage temperature range of -20 ~ 60°C . It's general features are summarized by Panelook in the following: WLED Backlight , for Apple iMac. Based on its features, Panelook recommend that this model be applied to Desktop Monitor etc. Now this model is in production. There are 1 items stock and 2 suppliers of this model on Panelook. We inputted this model's specification on Dec 20 2017 for the first time.