I dont think there is anything wrong with going IOS at all, there is zero risk of iPhone use dropping over the next 10 years, if anything it's increasing.

I would love to use my iPhone for navigation, (aside from the possibility of calls and text messages). I have been using LK8000 lately and it's fantastic, but of course no iPhone version so I am forced to use my clunky PNA which I can barely see in sunlight.

My iphone is so much smaller and brighter, it would be a joy to use... and it's always in my pocket so snapping it into a mount on my glider would just be as simple as it gets. So in my opinion you have a hole to fill if you want to continue to try to fill it.