Personally I think daggers should be usable in the off-hand no matter what your main hand weapon's properties are. Rapier+Dagger was a widely used and popular combo for dueling, after all. It is weird that it is entirely impossible with the current system.
It would also make daggers relevant as right now I can't think of a good reason to use a dagger in your offhand over a shortsword which just plain has better damage.
