Collections are not very useful, and are difficult to access from interfaces other than computers.
I think Plex should support a Tree Structure in the Libraries List.
For Example :
MOVIES
-Ultra High Definition
-High Definition
-Standard Definition
VIDEOS
-Music Videos
-Home Videos
-Documentaries
-Tutorials
-Nature & The Natural World
-Scientific
-Sporting
MUSIC
-Dance
-Classical
-My Favourites
This tree structure should be at least 2 levels deep (1 Parent, Many Children)
3 or 4 levels deep would be even more useful.