iOS 10.3 only has a couple major user-facing features, but it will have one very welcome addition for CarPlay users.
While people won't see a lot in the way of shiny new features with iOS 10.3, with the most compelling the update will bring with it a nice addition for CarPlay users. While opening apps when you're driving is currently cumbersome (and unsafe!), Apple has added a quick app switcher to the in-dash system in iOS 10.3.
In CarPlay on iOS 10.3, Apple has moved the clock and wireless status indicators from the center of their side of the display to the bottom corner of that side. This leaves room for three car app icons to appear on that side as well, but in the top corner. The top icon will be your current app, while below that will reside your two most recent apps. Just tap the icons to jump between the apps.
This will be a welcome change for CarPlay users. Currently, if you want to switch between apps, you need to tap the virtual Home button and choose an app. You might even need to swipe to the next Home screen to find the app you're looking for. All of this wastes time and is, more importantly, distracting. Many drivers only need to switch between apps like Maps and Music in any case, so this new system will make that easier, and will hopefully lead to safer driving overall.