I understand completely that modern engines suffer less from cold start than older engines, but this put aside: If for some reason the engine won't start, you're stuck, there's no means of putting the gearbox in N and being towed away?

That is what the key in the trunk is for (that you stick into the left cupholder).

I thought that was to manually release the parking brake, so this also puts the gearbox in N?

You use the key in the left side of the trunk (inside the panel) to release the parking brake. You use the key in the cup holder to release the transmission lock.

Exactly! On the many occasions that my '07 E70 was stuck dead in the garage, I had to manually release the E-brake & the tramsmission. Funny, the first time my '07 was stuck in the garage, BMW roadside had no idea how to release either the E-brake or the tranny! I had to figure it out and do it myself!