I don't think curved screens will really end up being a huge big thing. More like 3D screens. Remember those?
Face recognition could be, if it worked more reliably and wasn't so easily defeated. In this time of such expansive social networking, securing a photograph of a phone owner's face is far easier than lifting their fingerprint.
The fingerprint scanner isn't a big thing, in my opinion... But it works so well, it's use just blends in to the point you barely realize you're using it... Until you have to use a device without it,
I think the Moto X's "always on" speech recognition and GoogleNow are moving in the right direction. Touch free voice control could be another one of those features, where it just works and blends in to the overall user experience.
I also think the language coprocessor in the Moto X, and M7 coprocessor in the iPhone 5S, are also moving in the right direction. Compartmentalizing certain tasks and processes that run in the background to their own low energy processors can open a whole new world up for what a phone can do without destroying battery life. This can also let manufacturers reduce battery size, and make phones lighter and thinner, while maintaining or improving on the current expectations for battery performance.
We've also only scratched the surface of what 64-bit processing will do to the mobile landscape. That's the current thing that hasn't even been fully realized yet, and when it is, I think it will be the "next" big thing... It just so happens that the foundations are already being laid today.