The split started to happen about 5 years ago and it's really picked up velocity in the last year or two, to where it's getting hard to "jump" if you want to change. It's one of those slow, long-term things that's easy to miss if you aren't paying attention.

I think Udacity has a good model for this. I'm a generalist dev who has let curiosity drive my career more than anything else and feel I'm paying the penalty for it. Most places seem to want 5+ years specialization in whatever you're applying for if you're coming in at the senior level.

It's getting harder asking people to trust you if your resume isn't properly "tracked" into one specialty. I think that's a huge loss in terms of diversity and cross-skilling but perhaps necessary given the immense amount of sheer knowledge there is in each area, e.g. the entire iOS or Android API set.

This is just a return to the norm.