This is not a new rule. The following has been in the Specifications section of the BCA Rule Book for as long as I remember:
"The cue tip may not be of a material that can scratch or damage the addressed ball. The cue tip on any stick must be composed of a piece of specially processed leather or other fibrous or pliable material that extends the natural line of the shaft end of the cue and contacts the cue ball when the shot is executed."
It has been there since before Phenolic tips came into popularity. And while it does not mention phenolic specifically it uses two words (fibrous, pliable) that, in this context, would not be expected to be used to describe phenolic. To me it seems to decree a material whose texture and 'feel' are similar to leather. The spec has just not often been enforced before. There is a lot of conversation in the industry that it may be time to update and enforce the specifications. The situation with scarred or cracked cue balls is drawing a lot of attention at the moment.
Quite a few people think we need a 'measuring device' such as a durometer at every event with a number that the tip cannot exceed. Well, last I checked, durometers aren't real cheap. And they can be used incorrectly and give bad results. We used them in the printing industry to measure the hardness of printing blankets and two pressman on the same blanket would get two different results.
How about this? Leave it to the discretion of the Tournament Director? Every TD knows when a tip that he inspects is made to obey the spirit of the description or designed to skirt the edges and get over on the spec. Let them decide. No one who presents a true leather tip will have a problem, only those attempting to 'lawyer' the rule. Simple. I like simple.