Mod authors would literally have to reprogram their mods to work on Epic. All authors would have to reprogram their mods for Epic and manually upload those mods to Epic after fixing them. Well, most mods that servers use are outdated, abandoned, with years like 2017/2018 being their last update, and they are simply used because they still work. The only person who can update a mod is the original author, because of the way mods are coded/compiled when released.