Marissa from Google posted in the YouTube Help forums that if you want to beta test new versions of the YouTube app before they are released, you can.
They opened a method for iOS users to test new versions of the app using TestFlight, the iOS beta testing platform.
Marissa gave these instructions:
- Sign up for TestFlight here. Note: there are a limited number of slots available, so you may be added to a waitlist.
- Wait for a message from the iTunes Store that a new version of the app is available
- Download TestFlight onto your iPhone, iPad or iPod Touch
- Install the new YouTube version
- Use YouTube just like you normally would! Be sure to report any issues through the app (Menu > Feedback)
- Be sure to stay updated to the latest version. Users who do not stay updated may be removed from TestFlight at YouTube's discretion (since there are a limited number of slots)
Have fun and be brave.
Forum discussion at YouTube Help.