PS: Nice here refers to the French town (compare to Berne Convention, Geneva Convention, Treaty of Paris), not the common meaning in English.
1. Release it as youtube.js for the name recognition
2. Wait for the certified letter
3. Announce you're renaming your project and get another 24 hours of exposure in the news
This guy is playing the game.
https://github.com/LuanRT/YouTube.js#disclaimer
edit: why am i getting downvoted?
My advice to avoid any negative attention from YT/Google (but again IANAL) would be to do two things:
1. Move the "this is an unofficial" disclaimer at the top and bold and/or italic it so it's totally unmissable. I would use the same approach as MarshallOfSound: https://github.com/MarshallOfSound/Google-Play-Music-Desktop...
2. Praise Youtube/Google for having such a great API that empowers and enables their users to get the most out of their subscription. Make sure to point out the (true) benefits that YT gets from having a library like this that is available but they don't have to maintain and promise nothing to.