If we're proposing theme I got a few idea too.
-Prc based on a specific spell or power of choice (like the force missile mage or the constructor)
-Prc based based on having a companion (animal companion, familliar, special mount, etc...)
-Hybrid theory 3 (perhaps too soon ?)
-Prc based on teamwork (aura, bardic music, teamwork benefit, etc...)