Would it be possible to rework the IDE files such that they can be integrated directly into the newest arduino 1.6 as a new core?
The ESP8266 (well known cheap Wifi chip) has recently been included as a new core, and it runs perfectly with it's own toolchain. You can find it on the arduino-esp8266 github , and a forum discussion on the arduino-esp8266 here.
The new core can be added to an existing arduino 1.6.4 installation by running the board manager after adding a board related JSON file to the Arduino preferences. The hardware specific files and tools (containing the toolchain) folders are then automatically downloaded and installed into C:\Users\xxxx\AppData\Roaming\Arduino15. A restart from the IDE then shows up the new board and tools.
I believe that the same procedure for the NavSpark, with the Leon3 toolchain will probably not be that different from the ESP8266 implementation.