Not impossible no. But if the people say the sword comes from nowhere. Just think if you make cross unsheath. It will be clipping at some points, thats not the best solution afterall. Also it would need a lot of work and i don't know if anyone will do it because is it really that game breaking?
I think you're getting too technical and picky, It isn't OK to see clipping and I don't like it most times, but 2h warriors can sit down in chairs with the 2H weapons sheathed, clipping through the chairs. Like the vid I gave from DA:O. Your complaint is that injurious possibilities and implausible body functions make it seem unreal, yet the video makes it look natural and movements normal. Again, "suspension of disbelief". Here you want the ability to see where the second sword in a dual-wielding role as displayed on the body, yet complain (through my example as I wasn't talking about the mechanics, just the looks) that any sheathing of dual-swords by any location on the body makes it injurious or implausible. So, which do you want? Because if you don't like the implausible ideas, then only having one visible is the way to go. Sounds to me like you're having a bout with cognitive dissonance.