Are there any locking options that lock the drive train of a bicycle? I've been looking into the different kind of locks available, and came upon this short documentary about bike thefts in London. Seems that just about any lock on the market can be easily beaten by a large enough set of bolt cutters. So I was trying to think of a better system, and I thought of something: Why not have locks that are built into the bike itself? Something that locks out the drive train in some way? 

It seems that in the majority of thefts, the thieves are riding away on the bike. From about 10 minutes of pondering the question, it seems like a small hole could be placed in the crank axle without compromising the strength too much, and then you could incorporate the locking mechanism into the down tube. When the bike is locked, the cranks can no longer turn. 

Searching on the internet yielded no results for locks that lock the drive train of the bike. Is it just an unworkable idea, or has nobody thought of it until now?  

You would still have to lock the bike to a rack to ensure that someone doesn't just carry it away or put it on the back of a truck.  But it would make the bike that much less of a target if the thief knew that such a system was in place.
Wheel locks are an implementation of this idea. They simply prevent the rear wheel from turning, which is effectively the same thing.

Again, any thief with large enough bolt cutters will be able to effectively sidestep the problem without hassle. But worse than that, the odds of your bike being stolen while being immobilized like this are still orders of magnitude higher than locking your bike to something with a U-lock. Any thief can merely pick up the bike and run off with it (which is more doable than you'd think) or toss it into the bed of a pickup and be gone.

And that's simply what it comes down to. Locking the drivetrain doesn't provide any additional mechanism that a prepared thief wouldn't already be able to work around, and, while better than leaving your bike totally unlocked, is still far less safe than a U-lock.