In keeping with shortening the amount of time you can lock someone up for (4 years here max, vs 6 in NBA) I think we should have first 2 years guaranteed, 3rd year optional, then 4th year the player is a restricted free agent where anyone can bid on him but the original team has an option to match.
I guess the other problem would be if no one wants to bid something i guess it makes it harder to determine how much this player may actually be worth, but i guess that comes down to the market. Although, if, for instance, Blake Griffin by the end of his rookie scale should be worth a max contract, but no one can afford to pay him anything close to that, his current team could sign him to just a bit more than the MLE and get him for next to nothing and kill the league. That def is something to keep in mind, and really should have some effect on the player. Maybe find the players value range, and compare the price of other players around that value and say that the average should be their minimum or something like that.