Shop items should (imo) be on the global loot list with something like a half percentage(or lower?) drop rate. It would add excitement to my game play, allow you to say all loot is available in game, and if the drop rate is correct it should sell more cosmetics. Ty 
Someones played Marvel Heroes.
keep dreaming. shop cosmetics will never be drops
Shop cosmetics will never drop and they will always look better than all the free stuff in the game (not very hard, all the free stuff looks like the player is nothing more than an NPC).
The only cosmetics I could see dropping in game would be the giveaway cosmetics, such as from twitch streams or the KFC thing for example. Although they’ve already started to give away the twitch streams in the in-game shop already. So yea, sorry about your luck. They definitely won’t give up a source of revenue that is completely optional to purchase to be allowed to drop within the game, even if the drop rate was 1% of the uber unique drop rate outside of Duriel.
I LOVED Marvel Heroes and I do support the OPs idea… Even if the drop rate is something like Uber drops in the World (not Duriel).