From that idea.
At the moment, it is not possible filter pages on a watchlist by a personal key: article I'm working on now, community pages about sport, pictures that I have changed the description...
Have a way to tag pages added to the watchlist with some personal tags. Those tags are unique to the user and would complete other filtering options very well. Users can then filter by personal tags (and categories, namespaces type of edits... by potentially excluding them (T174349)) and save those filtered queries.
This would also solve the need of T3492: Multiple watchlists, a community whishlist item in 2015, 2016 and 2017.