The problem with that is teams can cut players under contract so you have to leave players an equal chance. What agents have done is elevate guaranteed money as a result to protect against cuts. What teams need to do is work in lock in clauses where holding out is really costly (just like cutting a player with a lot of guaranteed money leads to costly dead money)

You'd have to have an automatic decrease in future salary from a hold out. So right now Donald's salary next two years would drop to the minimum. Unfortunately contract terms in regards to years and salary are part of CBA so doubt they could even do that.

So basically there needs to be something worked in to protect owners against hold outs in the same way that guaranteed money works against them.