Take this as a user reply rather than a Trakt staff reply 
as to not to take away from the feature request - I can see some value in a dedicated section if many others agree.
Your best alternative right now would be to use Personal Notes. Either specifically on the item itself (which is what I use myself), or you could add to a list and include it as a note on that list item, or you can rate it (doesn’t have to be marked watched, and some people may dislike that but IMO it seems fine to rate an incomplete movie) and add a note to that specific rating.
Adding the note to the specific item would have it appear throughout the apps and website and on the actual summary page if you revisited the page of the movie. The others only within the list, or profile’s notes section.
Depending how or how often you need to view/manage these ‘notes’ probably goes to the option you choose.
- if you don’t care to see them all together, then an item note fits best.
- if you want to see them all together, a dedicated list probably makes more sense.
- if you want to apply ratings to all, and see them all but otherwise they could be mixed with other rating notes, a rating note makes most sense and you could even add a consistent ‘tag’ to those specific notes so that you could filter your rating notes (eg. add “PW” for ‘partially watched’ and filter by that: https://trakt.tv/users/ohifriend/notes/ratings/added/asc?terms=PW.