I feel stupid, but I am in the iPad app, and have tried holding down on a channel in "On now" and never get a "manage channel" or "add to favorites" option -- I have spent the last 10 mins looking for how to do it and gave up.
Is this feature missing in the iPad version? Am I "holding it wrong?" 
Try under Settings > Manage Sources > Source
Thank you -- I would never have thought to look there.
Also consider Channel Collections. It lets you create collections of channels like Favorites or other categories on the server, and will sync down to every client or just the ones you would like them to apply to.
This was a bug. The options to hide channels, add to favorites, etc have been added back and will be available in the next TestFlight beta.