Gearboxes are seeing a little bit of usage on Mountain Bikes, this is largely around moving weight to the 'sprung' part of the bike to improve suspension performance and also protection/maintenance advantages
They still have resistance/efficiency and cost disadvantage though
https://pinion.eu/en/
Think you meant unsprung weight, yeah? The Pinion system seems to move a lot of complexity to the bottom bracket, which is generally on the unsprung part of the bike, the same as you would move weight away from the wheels on a car so they can stay attached to the road more of the time.
