I don't buy the motor doping story. I have never seen a hub or a crank where a possible engine is at such a low weight that it would make sense to fit it in. Can anyone provide a link where such a device exists and perhaps weighs around 500gr (that would mean shaving off 500gr elsewhere on an already lean bike).
The motor theories often enough presume that there are no, or fake inspections. So, in this line of reasoning, I guess weight shouldn't be the issue either. Yet it has to be mentioned, that bikes can be much leaner, and much leaner bikes exist, it's just that the UCI has set a specific minimum weight. So I think getting rid of it should not be that hard I guess.