In some of the recent updates, most of the backpacks have been patched so that weapons no longer appear behind them. Backpacks like the Black Dragonscale Backpack from Wrathion no longer show your weapons behind it.
Now, for classes such as a fury warrior, where we have two gigantic swords on our back that overlap and form into each other it creates a very ugly mess of textures on our back that we are constantly forced to look at as we play. The backpack was a great tool for hiding this mess while still allowing us to display our weapons. It also added to some immersion due to it looking as if the weapons were sheathed behind the backpack and not stuck inside of it itself.
Now, this doesn’t apply as neatly to all backpacks. But I believe the players should have a choice on the matter of displaying their weapons with the backpack or not. This could in the transmog screen on said backpacking. When right-clicking the backpack it could allow you to select to display weapons or not. And then apply that selection. This menu is already included for several weapons that have multiple copies collected. This is something fairly important to me, especially as a fury warrior. I hope to see this added!