I know I don't have the money nor manpower to make my dream games come to life, but I think that if more games were moddable or even open-source, the game industry would begin booming. By making every part of the game moddable, including the deepest parts like core mechanics & gameplay, people would be given absolute freedom.
The first step to do this is to have the game use common formats like wav, obj, png, fbx, cpp, blend, etc.
This gives the end user an easier approach to modding since all he has to do is use common software to make something new.The game must be coded to use every resource that appears in the folder. This is a dynamic system and one example of this is The Sims 1 (2000), which would load any new file added to the games folder along with the pre-packaged files.
All mods must be released under CC-BY. This will benefit the entire community as they will be able to examine mods and release bugfixes if the original creator does not have the time to do so. Collaboration is an essential thing in modding.
Allowing people to create custom sections of different features is an absolute must. For instance, custom radio stations, custom TV channels, custom categories, subfolders, etc. This helps people enjoy what they like in an organized way. This feature must be implemented via adding extra folders and possibly an xml file to fill in the metadata.
Addition is essential. People generally don't like replacing things unless they want to. So adding on to the list of things already in the game is something that is crucial to modding.
This might be very difficult, but mods should be coded to automatically patch along with game updates. This saves people the trouble of mods breaking all the time.
Graphics should be the last thing to work on. They don't mean jack if the game is broken. Besides, if people don't like the graphics, they can always make an ENB. Minecraft is a perfect example of this.
Procedural animation has shown to be better than predefined, as procedural adapts to the size and shape of objects.
Now, with all this said, I'd like to show you a number of ideas for games that'd definitely get people interested, along with listing moddable features that would be key to making it great. These in the list are add, not replace
† = Extra Note
-GTA-like game | Vehicles, Pedestrians, Weapons, Body Shop (Cars), Restaurants, Radio, Safehouse, Garage
† In terms of vehicles, things that should also be included is giant ships (ex. Cruise liners), UFOs and unusual vehicles.
-The Sims | Pretty much everything
-Need For Speed
† Big rigs should be a class of cars added
-Skateboarding (a la Tony Hawk) | Skateboards, Music, Create-A-Modes (Park, Goal, Graffiti, Sticker, etc.)
† Created Goals should have people be allowed to tweak everything. Examples are goal types, character voice, animation (this includes transitions).
† Created parks should not only have many different base environments and sizes, but should be able to use any and every piece from normal levels as well
† People should be able to create things like custom grind markers. They should also be able to make custom gaps, as some are very unique and not able to be made in the regular CAP mode.
† Custom World Destruction Tour (Tony Hawk’s Underground 2) events should be able to be made.
Wrestling | CAW Outfit Parts, Music, Videos, Animations, Roster, Create-An-Entrance, Etc.
† Custom Music is a must.
† Pyro and Lighting should not be restricted to sections in Advanced Entrance mode. It's unrealistic if fog suddenly blinks out of existence.