The problem with iOS development, as I see it, is that it's too device specific—likewise with developing for any specific mobile platform.
It seems that backend development skills are more marketable than front end—no matter what the language. Perhaps the same applies to those who can develop desktop apps ... though ideally, you'd be able to do this for multiple OSes.
I'd maybe look at (in descending order)
- Desktop app development
- Backend web development
- Front end development (HTML, CSS, JS) perhaps with a focus on cross-platform apps based on web technologies.
(I'm talking through my hat here, though, as I'm only really familiar with front end coding, with only the rudiments of JS—something I'm trying to address.)