Adding a list to the watchlist is essentially adopting a personal list. When I add a list to my watchlist it should be treated just like an official list. For instance...

1. A movie's INFO tab shows all the official lists which include that film. This should be expanded to show if the movie is in any lists added to my watchlists.

2. The Progress page should have an additional tab, "Watchlists", which shows my progress on any lists in my watchlist.

3. Official lists give trophies but completing an "unofficial list" would award an "emblem" which would essentially be the avatar of the list. The would be on a separate awards tab.

These are all manageable improvements that will provide a customizable user experience and also takes pressure off of adding more official lists (sometimes more isn't better if the whole thing becomes too unwieldy)