I suggested this as sarcasm in another post, but then I realized....why not suggest it? Lets see how OP everyone thinks this is....
Incendiary Missile: Each tick gives you a counter that makes your next rail shot do 25% more damage. Stacks up to 4 times
Thermal Detonator: Causes your next Railshot to be an auto-crit
-When Incendiary Missile and Fusion Missile are both applied to the same target, that target becomes snared for the duration that both DoTs are active. (If one DoT ends, the snare ends)
(the next 2 suggestions involve damage so they are very unlikely to even be considered)
-When Incendiary Missile and Fusion Missile are both applied to the same target, increase the damage of one or both DoTs.
-Further increase damage done to double burning targets. Similar to the skill box that causes 10% damage bonus to burning targets when using Rail Shot, etc. (Except this increase of damage only applies when both DoTs are active)
Feel you were much closer with the changes to IR and HiB. It wouldn't be more OP than Smash is to be honest. I like it.