Planetary gears, this time. Sealed into the bottom bracket of course. And no, not for the first time! Still, it's a good idea, especially when you run in mud, dust and grit. The downsides will as always be weight, weight and weight, followed by serviceability, longevity and, yes, weight again. You can throw in friction losses as well, but that may be quite minor compared with, umm, weight. We shall of course see!
Nuseti mountain bike features a sealed drivetrain