This is a difficult one - if there were a clear example then no doubt the ArbCom would have given one, despite there being many Arbitrators who could have proposed ideas. No doubt they were mindful that no suggestion made by the community to date had come close to reaching consensus. I'm also mindful that a proposal to leave date notation questions to the talk pages of individual articles also failed to gain community consensus, largely as there was no appetite to repeat the same arguments over a large number of articles. I think a "substantial reason for the change" would be if it was consistent with a proposal discussed community-wide that gained consensus. However, I don't see any proposal gaining this consensus at present. Another reason would be if it were a change that was so obvious that no-one would rationally oppose it - again I can't think of a real-life example here,