This is just a suggestion but I think it would be really cool to have that feel when playing Isengard that all of the upgrades and different powers of Heroes revolve around Saruman as he was indeed the driving force behind all the power of Isengard itself.
Here's a couple of suggestions:
Make Saruman similar to Sauron with 2 skillsets.
Skillset 1:
Power of Speech (passively grants all troops on map 10% movement speed and 10% experience/Damage)
Fuel the fires (Lumber Mills produce 10% more efficiently)
Unprecedented Knowledge (enables training of Mines when used on Siege Works, Enables use of Heavy Armor/Forged blades for which now cost 50% less as well when used on Forge, Gives Grima ability to use Dominate Hero)
Ring Maker (maybe some cool suggestions)
Skillset 2 is the same current one.