[NwtnsMthd]

200W at 300g is realistic for a modern BLDC motor. The article states that Maxon was the motor supplier so they likely used the EC-4pole series, I'm guessing it's one of these.

https://www.maxongroup.us/medias/sys_master/root/88825569607...

It's 30mm diameter to fit in a down-tube, 200W, and 300g. But just because it's 200W doesn't mean you have to run it at maximum capacity, there's no reason you couldn't run it at 5-50W.