This has never bothered me truly but i always assumed that when double wielding blades, you would also have 2 scabbards, one on either side of your body, so i was sort of dissapointed when the game was released and i found you only have 1 and you pull your other blade from no where... i even think it would look awesome if you had one blade on your side and the other blade/scabbard on your back, since nothings going on there...

What do you guys think? Would it be too hard to add another scabbard or visible blade when dual wielding?

There is a mod that does this. So it's no too hard, but it's doable.

They ran out of time.

Seems like something that could've been incorporate in about a weekend, along with underwater combat or non-human children..
Far easier to implement than mounted combat.

I'm surprised they haven't put it in a patch.

I would also love the option to sheath a 1-handed sword on your back.

This sort of thing would be a far better option for a weapon like the Scimitar, which looks so awkward sheathed at the hip.