Apple have submitted a new patent which shows a different kind of headphone jack which won't be compatible with the current 3.5mm standard.
Iphone
The new connector is labeled the D jack and it is only 2.0mm in diameter which could suggest that Apple are pushing for an even slimmer iPhone. it won't be a big surprise if Apple go ahead and use this unique headphone jack in an upcoming iPhone as in the past they've always gone with their own unique connectors, showing little concern for conventions.
The patent was filed in 2011 and has only recently been released publicly. With the iPhone 6S range recently announced, it seems natural that next year we can anticipate an iPhone 7. With that, comes a much grander redesign, and perhaps we'll see this new headphone jack incorporated.
This of course is all speculation. As mentioned earlier, Apple aren't shy about forcing users to have additional connectors and adapters to suit their design, but the ever-increasing popularity of Apple products suggests that this doesn't bother the average consumer all that much.