Uh, well, because the pandaren are supposed to be on the same level as the player models maybe? They don't seem to have the extreme amounts of customization mentioned in this thread and I don't believe that they would suddenly at it in. Plus, worgen and goblins aren't confirmed to get an update yet, so.. they would have to edit it so they can add more customization to the pandaren models, and to the goblin and worgen models?
Yeah, no. I very much doubt it. If they were planning to add more customization, you would have seen it on the pandaren.