A new block, maybe something like "Lightning Transformer", or "Lightning Receiver" when a lightning rod is placed on it, during thunderstorms when struck it could create a LOT of energy.

BONUS: Upgrading the Tesla Coil block by customizing the strength and distance, this would be good for striking entities and metal blocks within a radius, this would be VERY expensive power wise, as this could charge creepers, and transform pigs and villagers (Only at max strength). Perhaps the strength of the effect could be modified too, allowing for less damaging effects like simple shocks. (This obviously wouldn't be required for the first part of the suggestion to work, I just figured it'd be cool to mess around with)

However, being able to create witches, pigmen, and charged creepers using this would potentially be overpowered, the vanilla farms are way more technically advanced, which is some cases aren't that fun to create. Even if you made a villager breeder based witch farm, it'd be vastly less efficient than the witch hut based version, but with this blocks functionality you're simply giving control over lightning, which is especially helpful in worlds with poor rain frequencies.