WHAAAT???! take something simple and…….

Having watched the video, it’s clear that the designer has been committed and thoughtful, and genuinely wants to solves a problem. He’s worked hard on it and deserves respect and time. Yes, a Rohloff doesn’t do the same thing, since it’s important in MTBs to get the unsprung weight down, and try to control suspension/chain tension interactions. The supre drive does have the problem of drag and a lot of additional exposed gubbins. It does do some of the things which a gearbox does, but not quite so well, since the cassette and mech remain part of the unsprung weight. And both the supre drive and a gearbox need dedicated frames. But you can’t fettle ratios very easily in gearboxes - although there are variants of inclined cone drives which do enable infinite variation in ratios (think DAF). Ultimately, the gearbox can develop a lot, and probably will do. Like many things bike, it will get lighter, stronger, cheaper.

I haven’t had a ‘problem’ with ordinary mechs for a very long time, even with quite long cage mechs on dinner plate cassettes. Yes, I have had cursed mechs which are a nightmare to set up but haven’t we all. They are quite refined now, and yet still simple enough - and carry multiple functions: changing gear, keeping chain tension during complex rear axle paths on FS.
 
top idler will need to take a high load! still has loads of chain slap, adds weight too! has good and bad points.
 
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