it is probably more interesting to ask how one forces severy player to implement this. By making players without this "feature" somehow illegal? Illegal to sell or distribute? Illegal to make? How one would enforce that. Also obtaining content by legally questionable means is essentialy same thing as using "illegal" player. Also it seems to me that it is easier to go after file sharers (there is somebody whose rights are violated) than after users/distributors/makers of some software (who exactly is victim of that?).