The current plan, according to 9to5Mac, is to announce the new computer at the end of October alongside OS X El Capitan with an early November release date. As indicated by code found in OS X El Capitan betas, the new 21.5 inch iMac will feature a screen resolution of 4096×2304, which is a big step up from the current model’s 1920×1080 resolution. Faster processors and improved color saturation can also be expected in the new desktop computer.
The price of this computer will likely raise due to the new display and faster internals similar to how the 5K 27 inch iMac raised the price of the standard model. However the new model will likely be in the same department the 5K iMac is, Apple may still keep the 1080P models around as a base line option, which would be great considering not every person int he world needs either 4 or 5K screens to do their work on.