They already do that on Skywars (on bedrock at least), and I think egg wars too..?
Correct me if I’m wrong on the egg wars thing
#Custom Item every week.
prime bramble
velvet summit
This is currently being discussed by the feedback team ✨
(FYI: Skywars has an item rotation already so the focus for this suggestion leans more towards adding a similar thing to eggwars)