The source code of the real-time operating system powering the Arduino 101 is now available - https://blog.arduino.cc/2016/04/21/intel-releases-the-arduino-101-firmware-source-code/
This is really good news, because now if you want is possible to add some custom extra features in low level part. This is the link of the github repo: https://github.com/01org/corelibs-arduino101