Doing so by nerfing the GUI, rather than by a proper gameplay mechanic, is surely just defining the first "essential mod that should have been in the game from the start".
Pretty sure he meant to tie this to a gameplay mechanic, not just a UI limitation.
i.e. : invoke the power of water, spend some AP, cast water spells. Switch to fire using another invocation, spend some AP, cast fire spells, etc.
Probably still needs some fleshing out, but it's not a bad idea. I like the idea of having a cost to switching to antagonist magic elemental powers in the middle of a situation.
