You know, it's not a problem on PC, but Gearbox might have a tough time on Xbox 360 with this DLC. As you probably know, Microsoft doesn't allow the user to download DLC content they don't own, even if it's content that's visual-only - to properly display players that DO own it. Additionally, title updates are not allowed to add significant amounts of game data. So what happens when a player using the Mechromancer joins the game of someone who doesn't own the DLC?
Are they going to have to separate players that do own DLC from those who do not? What happens when you want to join your friends and they don't have it? Sorry sir, they need to buy a thing just so they can properly see a couple of models (Gaige and Deathtrap) and skins?
Unless the Mechromancer textures and models are already on the disc (and it's the gameplay tweaking and skill point adjustments they've been working on the last few weeks)... but people will still likely complain about on-disc DLC, even if there's just no other real way to do it.
I think the textures and models are likely already included in the game files. And people who don't understand game development will freak out.