It's a change because this has nothing to do with minor league players or with pre-FA major league players.
So had this been in place last winter, for instance, the Mets could have offered Alonso a six-year FA contract whereas no other team could offer more than five. What it most resembles is what the NBA once called the 'Larry Bird Rule' which, similarly, gave a bargaining edge to the team the player was already on. The NBA did this because, in a sport that's more star-driven than any other one, they thought it was essential that a team be able to keep a player so identified with their organization. (aka: the old 'I can't imagine ______ in any other uniform" ploy)
Of course NBA superstars bounce around all the time now so I'm not sure it ever really served its stated purpose (of even if it was ever intended to). Nor am I sure how any of this will appeal to players. MLB is both proposing to cap the length of a contract the players can sign and also, less directly through caps, the amount of money in said contract.
oe: cross-posted with Grimm