Here are the possible variations that I see as possibly happening.
Xbox 360
Price cut of $50: garanteed (big impact to sales)
Price cut of $75: possible (huge impact to sales)
Price cut of $100 and or possibly axing the 4GB SKU: unlikely (massive impact to sales)
A revision to hardware (AKA slimmer version): unlikely (pretty big impact on sales)
Kinect effect will still be strong for 2012's holiday season especially with a $50 pricecut plus the 360 will probably still have very good deals during the holidays: very likely (huge impact on sales)
Also expect massive advertising especially in the Americas for the 360 in 2012. (Pretty big impact on sales)
Games that will provide a significant boost to hardware.
Halo 4: This will most likely have a special limited edtion console much like Halo Reach did so expect it to move some serious hardware.
Next COD: It seems most 360 version Call of Duty games have special consoles so expect a big increase in sales from this as well even if it doesn't have a special edition 360.
Kinect Star Wars: The significant boost from this will be mostly from the awesome special edition Star Wars 360, it will also drive Kinect sales higher.
GTA V: If this game releases this year you can expect a decent boost for the 360
Playstation 3
Price cut of $50: likely (big impact on sales)
Price cut of $75-100: very unlikely (huge-massive impact on sales)
A revision of hardware (PS3 slimmer): I'm 50/50 on this one. (big impact on sales)
Some good Move games may increase Move sales which could also increase PS3 sales also there will be some pretty good deals for the PS3 on the holidays. (big impact on sales)
Expect very strong advertising especially in Europe for the PS3 in 2012 (decent impact on sales)
Games that will provide a significant boost to hardware.
Next COD: Even though the PS3 version of COD almost never gets a special edition console expect a big increase due to this game.
GTA V: If this game releases this year you can expect a decent boost for the PS3.
It really depends on a quite a large number of things but I believe the 360 will just edge out the PS3 for the year.