Well to respond to the fellow who thought I was overreacting on account of the other upgrade cards that might be added in the set, these cards are only applicable to units that can take them. Not to standard, non-unique TIEs who Assault Missiles would hurt most. And yes, three TIE Advanced or four A-Wings all with Assault missiles would be a devastating force in the present tournament environment. Some lucky rolls give a player the opportunity to level an entire squadron in one turn's shooting with either of those builds.
As for why it couldn't be photocopied and sleeved, please refer to the tournament rules,
"Proxies are not allowed during tournament play, each player must use only the components included in official X-Wing products. Each ship must have the official ship base, official Ship and Upgrade cards and the correct, official ship model. "
That pretty clearly details why you can't bring Assault Missile proxies to a tournament, which is the only environment these will be a problem in anyway… as when playing with your friends you can just house-rule Assault Missiles as you like to keep your game's balance somewhere near where it is now. I certainly won't use them in friendly games because I think they're an addition to the game that only limits options instead of expanding on them, in that it severely limits the effectiveness of swarm armies, Rebel or Imperial and makes already questionably costed characters like Howlrunner never worth their entire points value.
As concentrating fire in a tight formation is right now the only thing that really makes an Imperial swarm work, I question the wisdom of a single 5 point upgrade card essentially removing a themely and interesting build from competitive play entirely… which severely frustrates me even moreso because I've been running a seven TIE list, not because 8 TIEs is the flavor of the month, but rather because I think it fits well with the theme and I enjoy the imposing look of having many ships on the table. From a game-design standpoint, one should not even CONSIDER adding a silver bullet counter of that power until the competitive metagame has had time to evolve and a strategy has proven completely unbeatable without it.
As I mentioned in the other thread, this isn't a CCG where the threat of that counter will limit someone's strategic options. In order to limit your opponent's deployment, you also have to be using Assault Missiles. That's what renders swarm lists unusable. If you do not pack them yourself, your opponent can deploy to maximize their fire and take out a ship in the first couple turns for an early advantage that will remain all game. Your only recourse is to take assault missiles as well to force your opponent to also deploy spread out so you can have a game on even footing.