Well, looking into the pace at which smartphones are getting into demand, people are tend to worry about the challenges that they will face in to mobile app testing. Also, according to the test automation trends of the year 2016, it is going to cross web test automation's craze. Mostly functional testing, security testing, compatibility testing, usability testing and performance testing will be the most challenging part of mobile app testing whether for iOS or Android. Though Android has a huge demand since a few years, you can see remarkably increase into the trend of testing those mobile devices too.
I am not sure whether you have given a thought on this or not, but, it is always great to have an automation tool on hand to help you perform mobile testing like a PRO because when it comes to regression testing, it helps in a great way. Appium, TestingWhiz, Robotium are my favorite ones. Only TestingWhiz comes with a codeless architecture among these.
Anyways, let me know if you need any more assistance.