Well, there are allready new cloth as DLCs available, but the only way to get them right now is using a reedem code that probably came with the code if you preordered it
in one of the participating stores or online shops.
So from technological side I guess it is possible to have additional stuff.
The pre-order bonuses are already on the disc, they're not DLC. All you're doing when you redeem the codes is unlocking access to them. (Look on the underside of the disc and you'll see a gap toward the edge and then more written data like a hidden track on an audio CD, there are quite a lot of games that have this and unfortunately for us gamers, we're being ripped off by it)
It is possible to have clothes and designs as DLC, it's also possible to have weapons and attachments too as well as more maps.
It does take time to develop and test them though and of course submitting them to Microsoft for approval before going on the marketplace.