Currently, if you have your back slot set to hidden, your kits will completely ignore that and place a huge, clunky and often ugly backpack on your back. For some characters, this completely destroys the armor look you are going for. For others, especially female toons, some of the kids clip horribly not only with the armor but also the toon itself (I believe its grenade kits that will consume the entire head of a human female engineer).
If the option exists to hide back slot items, I see no reason why kits should be exempt from this. I would be outstanding if those items respected the option that was chosen, and did not appear on the player’s back unless the player desired it.
I know of at least a few players on TC who would use kits a lot more since it would no longer destroy their character’s look.