Modding games is a popular sport, and very productive, since you don't have to code usually much, maybe some little additions only.
However, modding has its limits, as you are usually bound to a quite hardcoded game genre environment, unless you use Garry's Mod or something, but that has then it's own limits too with the engine features.
Since I am currenly building a GameLib FPS template for LEBuilder, these thoughts came up. What the template will do, is to create a simple FPS game with one mouseclick. After that, you can compile it, and it just works. You can open the level1.sbx or level2.sbx in Editor, and it just works. However, since the time critical game logic is done in C++, you can't play the game in Editor, but you can edit it in 3D WYSIWYG very well. I think that is good enough. LE3 Editor will be done that way anyway also.
From a modder's perspective, you basically create a vanilla game, and then you "mod" it with Editor. You don't necessarily have to code anything in C++, but you can, if you want. Nothing is hardcoded in GameLib, you can choose which commands to use and when, and you can even choose to write your own commands which you use as standard GameLib command replacements. The C++ part of coding gives an unlimited possibility to "mod" the game to your imagination, and time critical routines will never be a handicap, because it's C++. With Lua or other slower languages you might encounter problems with time critical routines.
If you don't want to learn C++, you can also ask me for new GameLib features in the Werkspace Forums, which I will then implement as Editor Thingoids or Models. So basically most feature requests from artists and modders are about adding new GameLib Thingoids to Editor, and I have then to check myself, if the vanilla FPS template C++ code needs also some additions. But you don't have to care about that, it's my job, and I love to do it.