Alongside a focus changing the summoning theme dependent on the component selected, I think it would also be kind of cool if certain components modified the Weapon Fire spell. For example, a frost gem, once selected by a magic focus, would consume the item upon casting Weapon Fire and, for that instance, change the spell theme to cold.
With the addition of the new elemental types (poison, earth, etc.) this could allow casters to access unique weapon fires without having them accessible in the start area.
Really like this suggestion
At least currently the theme element of your flame weapon/darkflame is meant to be a little more permanent of a choice. That could change, but I feel like a lot about casters is kinda fluidy and changeable at a whim, which is not my preference.
That aside, the idea in a vacuum is neat.
We used to have these during EFU:A, EFU:M and EFU:R but I think they were removed with the rework of alchemy. You could make elixirs which when you drank them, they changed your next casting of flame weapon to corrospond with the elixir.