There's this problem that people doesn't run into normally, that when you install a mod its blocks, objects, potions, etc are stored in the map registry, some data structure that links block name with the block ID used in the map.
This thing is great for a player that gets a modpack, goes to start a new map and boom! there it works, or migrating a map from a previous modpack version to the next (or players that join a server with blocks disabled? I may have not understood that use case). However, if a player (or modpack maker) has been adding and removing mods to test them for the modpack in a single map, or the mods have been changing over time while you keep playing the same map, the block registry will get filled with entries that are spending block IDs that could be used for real, working mods.
Could we please get a command that allows to remove the registry entries related to a mod, so that we can not only deinstall but "purge" it from a map?