Why not just point it to moviesandtv instead of dividing the conversation into separate movies and TV communities (it doesn't seem like anyone has requested that delineation), or pointing either one to a community no one's subscribed to?
There are currently 3 and 2 pinned posts on top of !movies@lemm.ee and !showsandmovies@lemm.ee respectively, merging them would have 5 pinned posts permanently on top.
Also, there are at least different posters, and commenters seem different as well. Mod teams are also different, quite a few people are only interested in movies and not shows and vice versa
The pinned posts seem like a solvable problem: just pin fewer posts. Point taken on different mod teams.
I'm not sure a significant number of people are interested in movies and not TV, and I'm not sure how that's known except perhaps by subscriber counts (but maybe there was a poll I missed?). I would start from the assumption that there's significant overlap, but I have no real way of verifying that.
I'm not opposed to the separation of movies and TV in principle. I'm mainly just concerned about how long it would take to rebuild that community.