I am not sure how I feel about allowing chamber reduces or full-length sub-gauge tube's. However, this not as "sudden" as it first appears. If I recall correctly, these devices have long been allowed for use in Damascus or twist barrels at the Southern SxS. While I think this is mostly superstitious, my observation has been that it is rarely seen on the course.
Also, note that there is no technical inspection of guns or ammunition. I have never seen a trapper check on this at any station over the 25 years I've attended. I sincerely hope that these events don't devolve into an "equipment race". These events have always been "self-policed" by sportsmen/women, in the spirit of using game guns. If this change encourages more participation, then it should be a good thing.