Sources with some knowledge of the matter suggest that Apple will not be interested in increasing the megapixel count of its next iPhone smartphone camera. Instead Apple will likely focus on improving the lens system and image quality.
Previous rumors suggested the iPhone 6 camera may be bumped to 10 MP with a faster F/1.8 aperture (the iPhone 5s is currently sporting an F/2.2 lens) so perhaps the aperture will remain.
Rumors are circulating that Apple will use swappable resin lenses for its iPhone 6. Other rumors have suggested optical image stabilization but seeing how Apple is doing some clever gyro-based software tricks in the iPhone 5s to avoid OIS it seems unlikely the company will change its mind in the next flagship.
If Apple indeed retains the 8 MP resolution which debuted on the iPhone 4S camera, it will go against the current trend of manufacturer increasing megapixel count in their smartphones' cameras recently.
According to KGI Securities analyst Ming-Chi Kuo 13 MP sensor shipments are higher than any other resolution - expected to be 65% of all high resolution components by the end of the year. The raise in demand is expected to continue well into 2015. According to Ming-Chi Kuo Sony has a 65.7% share of the market for 13+ MP sensors.
Sony is expected to produce a new 21 MP 1/2.4" sensor for the last quarter of the year. Could it star in the Xperia Z3? It seems likely considering Sony's six month flagship cycle.