After Apple announced that the next version of the iOS will not support a native YouTube App, Google has formally launched a replacement mobile app for Apple devices. App is available in Appstore as of this writing!
The new app is said to have improved search functionality and more sharing options. This app will let you subscribe to channels like what you do in the web version.
Google also cited that they are developing an optimized YouTube app for iPad. Having a Google-powered YouTube app in iOS means better support and services.