Dangling Plot Threads - There are so many of these in ongoing, serial storytelling like superhero comics. Set ups that never got paid off. Questions that never were answered. Writers leaving a book before they were ready or a book getting canceled too quickly.
What are some of the dangling X-Men plot threads that you are hoping get picked up some day and answered, resolved, and/or put to rest?
They could be character specific or overarching themes.