Loss of power to wheels?
 

Last night on the highway it felt like a driveshaft fell out,
Lost all Power to all wheels,
Sounded like a broken flexplate.
Sound went away when put shifter into park.
(Engine is fine.)
Car can be moved (pushed) while in Park.
Towed to Garage, waiting on report....

Any Guess?

If you can push the car while on "Park" then I would say it is your transmission .. good luck!

Car can be pushed while in park??! Thats definitely not good...Tranny..

Could be linkage, I wouldn't jump directly to trans failure. If the linkage is misaligned, you could easily move it in "Park" because it isn't. Does it start up in park/neutral?

Maybe a CV joint? Because when one blows, it immobilizes the vehicle as all power is diverted to the wheel with the least resistence. At least I was told that by the stealership.

It starts in Park, (didn't try Neutral)
When I shift to D it starts making a broken flexplate sound,
with no power to wheels in any gear. Like driveshaft was gone.
I was hoping it was a broken yoke or something else....

Ouch, not linkage then, see post #5.

maybe it is the transfer box

http://www.realoem.com/bmw/diagrams/v/e/107.png

The Verdict:
front "propeller" shaft,
damaged the splines in the transfer case, so that too....

Transmission is fine.

At least it wasn't the tranny! Good Luck with the repairs!