Yes the rep mentioned this as well, it allows teams already at the minimum weight to move weight around, making it more centralized, he also mentioned a benefit to lightening suspension parts specifically. As well teams struggling to hit the min weight with heavy riders such as Baz or Redding see a benefit as well. But yes this was the first test, I'm sure we will see them again at Phillip Island...
It?s Vinales versus Marquez | Motor Sport Magazine
They're probably having to add weight in other places though if they're losing weight in others. There's a minimum weight requirement with bike+rider so I'm sure it's more about centralization of mass rather than going on a diet. I'd be interested in seeing exactly what they're trying to do with this idea.
"Ducati’s GP17 appeared with a small box in the back of the seat hump. There was endless speculation about the contents of this box. Pramac Ducati rider Michele Pirro joked that it contained a hotdog and a fizzy drink. Others were sure it contained electronics kit. But why put that weight in the worst possible place – high up and at the rear of the bike?
Or could the box hold a chatter damper? Chatter is a common problem in bike racing – a harmonics mismatch caused by resonance from the tyres and chassis that causes a high-speed vibration between the tyres and the track, which can cause a catastrophic loss of grip. Adding a kilo at the extreme rear of the bike could damp out chatter, because the moment of inertia increases by the square of distance, so a small weight that far from the centre of the motorcycle would have a significant effect.
Marlboro Team Roberts learned this by coincidence in the late 1980s, during the very early years of datalogging. Wayne Rainey’s Yamaha YZR500 was equipped with a datalogger during practice, but not during the race, because it weighed a significant amount – about two kilos. Rainey would have a great two days of practice and go to bed full of confidence on Saturday night, while his mechanics removed the datalogger. The race would be completely different, Rainey would struggle with chatter, get beaten and return to his pit baffled. At first his crew thought he had got a bad tyre, but after three races they realised what was going on. The datalogger was housed in the set hump and cured any chatter.
Or could the box contain something even more magical? An engineer from a rival MotoGP team suggested it’s a box of winglets. No, really. He thinks the box contains a gyroscope designed to reduce wheelies, thus replacing the winglets that used front-end aero downforce to reduce wheelies.
According to this engineer, the gyroscope is positioned in the very centre of the bike as far back as it can possibly go, which is where it needs to be to have any effect. It must be heavy and spin forward at a very fast rate to affect the attitude of the bike during acceleration. Maybe Ducati uses tungsten, a heavy metal? Years ago HRC used tungsten plugs in their NSR500 crankshaft flywheels to increase or decrease gyroscopic effect.
The gyroscope might work something like an engine turbocharger, spinning at an incredibly high rate (between 80,000 and 200,000rpm is normal for a turbocharger). This gyroscope would obviously do a very different job – spinning forward to overcome the rearward rotation of the motorcycle as it wheelies. Most of us already know that a motorcycle with a forward-spinning crankshaft wheelies less than a bike with a rearward-spinning crank, due to torque reaction."