Alexei Baboulevitch is reimplementing the iOS keyboard:
I'm working on a 3rd party keyboard for iOS8 and I want it to look and feel as close as possible to Apple's keyboard. Unfortunately, it's not possible to access the keyboard view through code, so this is my attempt to imitate it by hand.
The development of this keyboard is fully open-source, so the project may not work at all times. At the present moment, the baseline functionality is there. Left to implement are special characters, Shift, multitouch, and improved graphics (including translucenty and dark mode).