The first thing I want to address is the elephant in the room, "The Notch," aka the unibrow. It's the black bar across the top of the new iPhone X that houses a range of sensors and cameras that make the new facial recognition features possible. On the iPhone X, there are also curved corners on the screen which use real estate that developers may see, but users won't because there are pixels cut off in those areas.
For the next month, the notch isn't a huge concern because no one is going to have an iPhone X yet, so you have a few weeks to get your app ready. Make sure your developers run your apps in the iPhone X emulator to see what impact the new screen may have on your users. A month from now this won't be an issue for most of your iOS users because the phone is more than $1,000. Additionally, the phone will be in the hands of customers who aren't as concerned with spending money on the newest, most-expensive device. It's fewer devices in the hands of high dollar shoppers. So, you might be surprised how much of your revenue comes from the people with these expensive phones.
The question is: How do you handle the notch?
Right now, it looks like, when the phone is in portrait orientation, the notch only impacts the status bar. That means if you follow the human interface guidelines (HIG) and don't use a full-screen app, you may be fine. In landscape mode, some of the demos show the notch cutting off part of full-screen videos. By default, videos won't expand edge-to-edge so you won't lose content until the user double taps the screen to expand the video. You don't need to be concerned with that too much, unless you have written your app so that it uses full-screen for various interaction. In that case, you may need to reconsider the placement of those controls because they may end up existing behind the notch, especially in landscape mode. For example, if you have the phone in landscape turned clockwise with the notch on the right, your scroll bar might be behind the notch. iOS 11 introduced the concept of 'safe area' layout guides. If your visible views are constrained to stay within the safe area, then you'll be fine, but your app will have borders that are the same color as your background color when the phone is in landscape orientation. iOS 11 also does something new with the status bar color when you have a navigation controller. If the navigation controller is a different color than your background, then the status bar will be a gradient that fades from the navigation color to the background color. The picture below illustrates this fade. The biggest lesson is not to mess with the status bar. I know some apps replace it with their own status bar, which is already a bad idea, but now it's even worse. Apple has declared it their own playground - don't sacrifice your user experience trying to change it. Ultimately, the notch could lead to significant testing and layout changes, but you need to start working now-you have a month.