One of the things people love about WoW is the ability to mod your game, something not common in online games, period. However, WoW only allows addons that are client-side only.This means it edits the user's game- and even saying that is a bit of a stretch- instead of the server. This means you can add, like, a menu to keep track of all the monsters aggro'd to you, or change your hud, among many other things.

While i think not all types of addons from WoW would apply to a game like this, many of them would, such as the ability to change the HUD. Who here remembers the old hud, whether or not they played back then? We all know that the new hud sucks pretty bad, right? It feels like a bootlegged WoW Default HUD, which in and of itself, isn't too great. I mean, it works, but it's annoying to not be able to see your health and shield easily. That's one reason so many HUD mods are available for WoW and TF2 and the like- Because the HUDs just don't cut it for competitive play. And it's the exact same reason so many people dislike the current HUD for Spiral knights. Or, perhaps, who remembers the old Anime-Final-Fantasy lookin' logo? Why not change it back to that using an addon? While it's a small thing, it's a nostalgiac thing, and having the option to do things like that just kinda make you feel warm and fuzzy inside.

Also, while this is a stretch, it could even go to the possibility of changing the player model or armor models for the user. I mean, all the models can't be stored server-side, so they must be in the client, right? Then if addons were a thing, you could have the ability to edit them! Though, like i said, that is a stretch. A loooooong one.

Now, i won't disagree, this can and will have negatives. Cheats will be a thing, but it just means you'd need people to moderate the mods found on this site. Heck, here's an idea. Make it so that every mod needs an ID number, that is in an uneditable text file, or even in the code for the mod. This means if you find a cheat mod, it can allow users of it to be banned, or better, for the mod itself to be banned and unusable. Should the mod not be updated or should it not have an ID, it will simply be unusable anyway. This means in every copy of the mod, the ID should be the same- So, no matter where it's downloaded from, it CAN be banned. Everything has a solution! Now, while it isn't foolproof, is anything?

So, tl;dr, have addons that work similar to WoW in that they only edit things that are held in the client. Make maps, however, not modabble. (Not Minimaps, i mean Areas) Duh.