.
The only issue I have with Backpacks is the same as Arrow Quivers, they tend to clip through bodies. If the backpack would not do that, I would use one. Then again, I play in First Person, so clipping issues on my character would not bug me, but I might see it on other PCs.
I would love a backpack. Especially if there were a few models of backpacks that displayed according to how much stuff you had in it.