i like the idea (i even made a thread suggesting it before), but i think your suggested implementation is a bit over-complicated. tying it into the operator/focus doesn't make a whole lot of thematic sense and adding more keybinds to toggle between augmented and un-augmented casts seems like more effort than is necessary, not to mention it'd be extremely inconvenient for console players.
i could definitely see special resource costs attached to augment infusion tho, i like that