I have two thoughts.
First, @DaveP043, the PGA Tour could request from the USGA a Local Rule or a "waiver" or whatever it's called. The USGA might just add it to the Model Local Rules. You can implement a bunch of Local Rules, the "Models" are just the ones you can copy/paste and don't really need "permission" to use.
If the PGA Tour bans them I imagine the USGA/R&A might adopt or help them craft the language for a new Model Local Rule.
The second thought is this: who cares what they've got written down if you enforce pace of play policies? Green reading charts aren't just used to putt - players use them in the fairways, or on the tees of par threes.
Writing a Local Rule against them may be difficult. If the true problem is "slow play" then fix that. If the true problem is "de-skilling" the game, then they may go the Local Rule route.
@ncates00, this topic ain't about arm lock putting, and nobody is saying "putting is easy." They're saying "green reading should be a skill" (with no real evidence that players who use green reading books putt any better than those who don't).