Link comment to item in lists
This would enable us to add a comment on for example why we added item X to list Y and then remove the comment when X is removed from Y. This would prove useful especially in watchlists.
It could also be useful in list of films/series we don't want to see where people could comment on an item and present arguments on why one should see/would enjoy this particular item.
I'm sure people would find other ways to use this