I would like to suggest a dedicated spell tool. Instead of placing spells in ordinary tools and guns, a dedicated tool for that job would solve the control issues currently existing in the game. As it stands, my impression is that fireballs are currently the strongest damage implement in the game - IF you have a macro that chains the R key and left mouse buttons in rapid sequence, which I doubt many people thought of. You can dish out up to one fireball per second, possibly depending on server ping (it seems to be slower sometimes). I would very much like to get rid of the dependence on a macro.
Might I suggest a kind of gauntlet, worn on the right hand over the glove, that rapid-fires the chosen spell on a left click and longer charged variants on a right one? Alternatively a kind of magic shield on the right mouse button?
I had a thought about this as well though my idea took me in a different direction. I think maybe an item that we can use as a magical ranged weapon like turning the bow into a weapon that instead of having different ammo types like the gun, we can cast spells on it and have the arrows produce spell effects when they hit.