[mchannon]

Based on Apple's latest overtures, OS X is becoming iOS far more than the reverse.

That said, any code and library base, be it Apple or otherwise, has a shelf life. It will eventually be replaced, just like the hardware it runs on. That said, there's still a need for good OS X apps today and well into the future. If they EOL'd it tomorrow, things'd be different.

2 years' experience as an iOS developer sounds just about as impressive as 3 years' experience. May as well get some breadth, but most of all, you might as well do what you enjoy doing.