Woudnt it be nice if shields gave you protection on back? The way it protects you when you block with it, or at least give bonus to armor against melee (like it gives right now against ranged).
1) This will add another element in character customization, u can have back protection, but it will reduce movement speed due to weight. There will be more sense having points in shield while playing polearm/2hander. And we will see a bit less of unshielded 2handers.
2) Also its realistic.