I read an article that suggested the move toward banning the shift is from the players. Freddie Freeman was making some comments about how it's not easy to change one's approach to go the other way because of how hard pitchers are throwing et cetera.
Then there's our old friend, MLB consultant Theo Epstein, who was hired to assist with possible refinements in the game, and I think this was one of the biggest issues he's been looking at.