How far have you gone? This was one of my many interests. I've looked at the app myself (partly decompile) and also was researching on its bluetooth protocol as a way to interface. Recently they've released the sdk for Loomo - their official robotics add-on that interfaces via USB. I just glimpsed on some of the demo codes in github. There might be some clues there. No joke but my primary interest is developing my own robot from modular parts - to appear driven by Furby (open furby), but uses a powerful odroid x4 (or powered by docker swarm FAAS - I built on pcDuinos sbc), vision AI via Intel Movidius usb and Google home mini for text to speech, and LG 360 for 360 camera viewing.  Since everything is modular joined by 3d printed custom frame,  they can easily be disassembled -- at least that is how envision it. Already have all the parts; I'm just lacking time and focus. :)  Btw, you do know that the segway mini pro was already hacked before via their app by a security researcher from ioactive? Hence that was my initial approach too. 

Are you located in Europe? I was thinking of hacking the Ninebot mini so that it could be controlled remotely over 3G/LTE.

What about using a flight controller like the APM/ArduPilot and creating an interface between the FC and the PCB on MiniPro? APM would let you create a 'flight plan' on a phone or laptop based on GPS and other position sensors.