Run and Gun would be proc'd off of Rocket Punch, which is only a 9 second cooldown. so if need be, every 9s you could use 3 casted abilities as instants. use all 3 in a row, and that is 4.5s, and Rocket Punch is halfway done its cooldown already.
i think it would be very well balanced, especially in conjunction with the relatively wimpy knockback on Rocket Punch for Arsenal. it would allow the merc to create additional space. and after 3x instant tracers, heatseeker missiles, rail shot, and explosive dart, your opponent should be pretty dang close to dead. at that point use jet boost, and finish them off.
I still see some problem with this. After all a sniper while being able to do that must stay still to nuke you down, If this change to rocket punch was implemented there would 0 chances for a meele class to ever kill a commando. I charge and you knock me back, root and start running away while insta casting. Now i have to get back to you with the leap in cooldown and after having eat 3 nukes straight in the face. Even if for some reason i make it there alive you still have the knockback and a stun, and obviously you can do that again, after all it has only 9 sec cd.
Sorry as much as i agree that the commando need something, this would make them the new FOTM.