To summarize this very long article:

Essentially smartphones are entering the laptop stages of ubiquity and market saturation and making people wonder whats next. Smartphones are also losing their wow factor and just becoming another "commodity".

People are also finding less reason to replace their smartphones and replace cycles are getting longer.

The only double-digit growth is in the lower priced segments in developing nations and whats stopping Apple and other giants is their reluctance to dilute their premium branding.