That would be my vote. I think it'd do some fascinating things. Perhaps the worst invention of the unions was seniority, not because of the rewards one gets from it but rather because seniority ends up being golden handcuffs. Allow me to elaborate.
What are the good things that seniority buys an employee? You get to bid on better routes, and you get guaranteed pay raises (sometimes). Oh, and you're less likely to be furloughed.
What does it buy the employer? You get to use those benefits to make the work rules less pleasant. After all, the employee won't leave...why start at the bottom of the seniority list when you've got 15 years with your current employer?
Wouldn't it be great if you could just tell your management to shove it when they make the work rules worse? After all, you could leave US for UA or DL or CO or AS or HP or whoever, without penalty. Certainly would make the employers more accountable, wouldn't it?
And wouldn't it be great if the deadwood employees, the ones with seniority that make the workloads harder on the good employees, got shown the door when times get tough? Better team of employees, happier customers, more revenue! It works well in other industries...