V5 has built-in support for programming it over Bluetooth so, I would imagine, they could expose an API for user control or a serial communication channel to third party applications as well.
But, there is, probably, not enough demand or business use case that would justify investing dev time into it (would be nice to have as an option, though).
We tried to experiment with controlling vex robot from a phone and the conclusion was that touch screen interface is nowhere near as convenient as an ordinary joysticks.
Although, it was nice to have a large display with capability to send back and show various debug information.
Also, you could define custom modal controls and annotated buttons for various infrequently used functions, but you can easily “annotate” your V5 controller buttons with some white tape and sharpie as well. 