Here’s a screenshot of the UCI’s rulebook, online at UCI.ch. Note rule 1.3.010 was introduced in 2005. Propulsion from any source other than your legs is banned.
Does motorised doping exist? Yes, it is possible the technology is out there. But is it being used in the pro peloton? Well there are only rumours and from now on, no rider will be able to get away with it. The weight, the noise, the hidden batteries: if everyone is now alert to the ruse, it cannot be used.