How the mod usually works is that either randomly or an outside source (discord or twitch chat) can pick effects that happen during the UHC that affect the players (flip camera, meteor rain, shuffle inventory etc). Some of these effects would not work well in a UHC or a mulitplayer setting, like the ones that pretty much kill you instantly, but I think most of the effects would definetly add another layer of problems and fun in a UHC. It would work as the base version of the mod, where it just picks a random effect out of the list and applies it to everyone at the same time.
It might be hard to implement on the technical side, I have no clue. I just thought it would be a neat idea so here I am.