How about an expansion of this to affect non-vehicle related ground fires as well? Since the game has a fire propagation system (that's just kind of gimped in vanilla but can be unlocked by tweaking fireFX.dat) it would make for some visually amazing forest etc. fires.
Or a variaton that would spawn FEAR-style lingering dust clouds from heavy gunfire. There's something like this in interior areas at the moment but the effect is not very strong and outside of story missions there are rarely any indoor shootouts.
Loving the effect so far btw.