It's a great trend, I think. Players are ordinary workers/asset owners and not slaves, so it is fair that they manage their labor, and not some “third parties”. It is clear that in the future we will still see cases where one club receives huge amounts of money simply for the fact that it breaks a contract with a player early, but in most cases the beneficiaries will be the players themselves.
I don't see anything wrong with a club taking huge money for the sale of a player. They have a contract with that player and if the player wants to leave the club that wants him has to pay the asking price. If the player stays and sees out his contract then that's a win-win for both the player, and clubs.
I also you like the idea of a "release clause". This helps the player gain some money from the sale too. Why I like it is because since the player has a contract with a club, if another club wants him, you have to trigger his release clause.