The airlines wanted the cap.  I do hope that this incident causes Congress and the Federal Dept of Transportation to reign in the airlines and stop the practice of overbooking and put in place procedures that have to be followed
when they want people to give up their seats such as what happened in this particular incident.  There should be no cap so that  maximum flexibility  is possible to induce people to give up their seats.  Kind of like a auction
where the financial inducement goes up until you have takers.
The other change that is needed is that once people are boarded, they cannot be threatened or forced to be bumped.  Any kind of bumping must be done prior to any passengers boarding.