Although this is the first time something like this has been found in competition, I can remember a few prior allegations or instances that many people have found suspicious. So I don't personally find this to be a complete shock.
One thing I find interesting, for road cycling at least, is that the UCI mandated weight minimums could make it easier for a rider to attempt something like this. Many of the bikes need weights in the seat tubes to bring them up to the minimum weight, so the extra weight of a motor and battery wouldn't stick out as much. If they were to lower the 6.8kg minimum, a bike with motor and battery might end up weighing noticeably more than the average bike in the peloton.
One thing I find interesting, for road cycling at least, is that the UCI mandated weight minimums could make it easier for a rider to attempt something like this. Many of the bikes need weights in the seat tubes to bring them up to the minimum weight, so the extra weight of a motor and battery wouldn't stick out as much. If they were to lower the 6.8kg minimum, a bike with motor and battery might end up weighing noticeably more than the average bike in the peloton.