You'd have to ask the dealer when it comes out. If it's possible, I imagine it'll cost about $2000 at least to do it. Different parts are more easily retrofitted than others. Distronic includes adding a radar sensor on the car. Depending on where BMW decides to mount it, you may have to replace a body panel or bumper or something which drives up the cost. That's also if the car's computer can be changed to also show the cruise control info. For example, you can retrofit the new LED tail lights on cars up as old as a 2002 (older ones need an extra computer part of some kind), but no one has yet been able to get the adaptive braking to work on the lights since the computer won't accept the change.
Basically, I wouldn't hold your breath on it.