Mobile developers are ironically stable, being forced to use the language of their platform and maybe whatever their companies cross platform layer is made out of. I've been doing ios dev for 4 to 5 years and it's only whatever is new for the new OS version in objective-c. I was paid to learn all the newness of ios 7 as I transitioned the app towards it. Swift is mostly objective-C in a new skin with welcome improvements, so learning it is easy.