A lot hinges on this magical contraption that can both accept connection and command, deliver power in sufficient amount when needed while being integrated into the hub, light enough to hide in a bike and somehow even be able to recharge. Have you seen the ebikes that they sell and the hubs that they have?

Now it could definitely work if you only care about a single attack - not even a full climb, but maybe 200-300m where you want to distance your rivals, but the risk (not just of discovery, but of malfunction, etc) just doesn't seem to be worth it. There's domestiques for a reason.