Does anyone know if this can be programmed to 2012 2013 cars? Would it replace the original smart key fob.

I don't think so... The key blade is a different style. Also, I don't know if the style pictured is really a smart key. I currently have a 2014 XF as a loaner and it has that key design, but it's not a full smart key. You still need to get the fob out and press the lock and unlock buttons, but the car does have push-button start once inside.

It might be possible if you keep the key blade separate, but I'm not sure.

Plus the XK has a slot in the armrest that takes the key in if your keyfob battery is dead so you can still run the car. But that wouldn't work if the key was a different size or shape.

That's weird, I just had a 2014 XF loaner as well and I never had to take the key out of my pocket, it was just like the XK, pulling the handle unlocked it and pressing the rubber button the the door handle locked it. Maybe for the XF it is an option like some other manufacturers?

When the new key design came out, I thought about it, but for the reason you cited I did not pursue it.