That is my worry. I started out using my iPhone 6 and my wife's 6+, but they were both too small for my viewing pleasure(eyes not as good as they once were). I could get by using those smaller devices but it takes the fun out of flying.
I'm sure I could juggle my iPad Mini and the Mavic's controller, but I just don't want to, and I'm sure it will be difficult devising a sun shade due to the location the screen is in relation to the controller.
I'm sure it isn't in the works, but a controller somewhere between the size of the P4's and the Mavic's would be neato where it would just accommodate an iPad Mini in the conventional location on the controller. This would defeat the "compact" design form factor, but it would get more old fogies like me to purchase a Mavic.
I'm still wowed by this DJI "selfie" drone, especially when I had no expectations above and beyond the offerings of the other companies. Too bad something like the controller puts me out of the market at this time.
But...those DJI goggles may be the perfect solution for me as well as others with similar eye problems. This will all be revealed in the coming weeks so we shall see.