I love the idea of the Unique Patrons from Blood of the Coven.
So I want to give an example of what I think would be a interesting way to do theme. I will be using the Infernal Contract Patron as an example, because I love Fiends.
Infernal Contract
Your power was brokered from a powerful daemon, demon, or devil to speed the corruption and moral decay of mortals. When you die, your soul goes to Abaddon, the Abyss, or Hell, and you can’t be raised or resurrected except by extraordinary means—though bold service may earn you a favored position in damnation.
Tradition: Divine/Arcane (Fiends are Divine but the Witch currently uses Arcane, Occult, Primal)
Misfortune Hex
Payment: Sacrifice - each day when you prepare spells, you must deal 1d6 points of damage to yourself as part of your infernal ritual, feeding the lost blood to your familiar. At 5th level and every 5 levels thereafter, this damage increases by 1d6.
Patron Lessons: Enchantment, Strength, Trickery, Vengeance
The Lessons each grant a new Hex and Spell.
I'm still playing around with the idea details.