You can only delete/hide purchases via a Mac or PC using iTunes, but yeah I agree that option would be nice to do via the ATV.
There is Music Playlists, there’s a selection of Playlists under the Browse tab.
Under the Library tab there’s also a Playlists section which will include all playlists you’ve added to your library.
I’ve got the shared playlist my wife put together for our wedding in mine as well as a playlist one of my kids put together.
You can create your own within the app by either selecting the three dots during playback or press and hold the trackpad over any title
No. WWDC generally introduces the Fall software releases. Feature requests at this level would not be discussed. Best to file a feedback form so Apple can consider it.