Rockets have fuel. They have less fuel the further they go. Fuel contributes to the explosion. Less fuel = less explosion = falloff. Some of the primary Explosive damage could be shifted to falloff Fire damage, changing the behavior of the gun at close range. It would still be as effective at destroying hull at mid range while losing hull damage at max range. It would lose a tiny bit of component braking at all ranges, but would gain balloon damage and a small amount of armor damage at closer ranges. However, the benefits of falloff are that now your Artemis shots can go as fast as they used to since Artspam can no longer easily destroy a hull at range.
You should read the linked thread. It would only effect its own new, third damage. As you said, not all guns would even need it. However, it would allow a great deal of fine-tuning to balance that the game desperately needs right now.