Is this supposed ban only for XC and gravel, or DH and enduro as well? DH rules for a long time have basically been that you need two wheels (and maybe brakes?), and that what makes it so cool. Road bike development has been stifled for decades because of the UCI, and I'd hate to see that mentality of prescriptive design come into DH. AON et al are some of the coolest setups, and limiting wheel size would be a step towards travel limits, weight limits, or geometry prescription like road bikes are.