In the UK I believe that the driving test (cars) is going to have a section on usage of GPS. The reason is to ensure that new drivers are able to drive the car safely while following GPS instructions AND paying attention to what is around them.
It seems appropriate to do the same for the PPL, as more people will be using these apps. It is not that hard to test, it could even be 'signed off' by the instructor. Just a simple nav triangle using a GPS device. Testing that the student can enter the route into the GPS, and use it to navigate safely. Possibly with the instructor 'simulating' the device breaking down or losing connection.