The physical proportions of the Knights don't really lend themselves to hip-mounted scabbards, particularly for the comparatively enormous high-level blades; you'd either have to auto-shrink sheathed weapons (which doesn't really work much better than vanishing them) or suffer hideous clipping and/or dragging a massive flipper-like scabbard around behind you. The size of high-level weapons is, I imagine, probably one of the reasons that blades disappear in Haven in the first place; their sheer massiveness makes them difficult to reconcile with the character's body shapes when they're not in-hand.

There's nothing wrong with hip-level scabbard! After all, they can just be bigger on the inside... =D

In all seriousness, this would be nice because it would add a further level of customization while in town. The scabbard or holster (for guns) does not have to be to the scale of the weapon while in clockworks, but it would add much more flavor to the toons while in town. In fact, you could go so far as to have certain blades be carried on the back (like the heavy sword lines), while light swords like the Flourish would be carried at the hip; guns could be holstered on the hip or in back.

Edit: Additionally, there is no need to make a draw animation, because you appear in the Clockworks with weapons at the ready, and in Haven weapons-safe.