Here's the information I've been able to glean from the forums so far:
Concept art of new warjacks
You can get a free Madelyn Corbeau, Ordic Courtesan, by pre-ordering Prime MKii
Warwitch Deneghra lost Dark Seduction
Warwitch Deneghra gained Influence
High Exemplar Kreoss lost Ignite
Destroyer loses 1 POW on the Executioner Axe
Destroyer's cost reduced to 9
Defile Sludge Cannon is now a spray
Defile now has a melee attack
Boundless Charge casting cost reduced by 1
Rules on remaining models (still missing some however)
Themed Army Lists
These have been reworked into a 4 tier system, where you gain bonuses for each tier you complete. Tiers are 'completed' by having the appropriate models (and only those models) in your army list. I'd put links to the known themed lists but then I'd have to sieve through 9 pages of random Retribution comments.
All this information was gained from an internet forum and should be deemed only semi-reliable. I'll correct any information that proves to be wrong as GenCon progresses.