The ISO 6-bolt pattern will only allow cogs as small as 16t, or 15t with special bolts. A better design would be a splined or slotted hub/cog interface with a few bolts holding it on rather than a lockring. Level is the only one doing this and it makes more sense than any of the other proprietary systems out there. No chance of slipping, stripped threads, or a lockring working loose, and the only tool it takes to change cogs is a tiny 1 inch long multi tool that fits in your jersey pocket.