I just published my first app. It isn't very good. I still consider myself in the learning process. What I find the most difficult is the UI/UX creation. How about you? What's the hardest thing about iOS development?
Right now my main concern is legacy code written in Objective-C. I have looked at taking a side project to maintain an app for someone but because it was written in Obj-C, I'm having some reservations. The good thing is that Xcode integration is the same for both Swift and Obj-C, but the syntax of Obj-C is very different.