I had this idea about game specific functions which can be tied to different shader properties. That would allow in game events to change shaders. Of course someone would have to provide these ingame function definitions, but this can be a downloadable feature, which the community can contribute like it's doing with shaders. The (ingame function -> shader) pair could also be community distributable like ini shader configs. How impossible would all of this be?
Also, sorry if this idea has already been suggested, seems kinda like an obvious suggestion, but I figured I'd share it.