I don't think it would displace anyone because the positions would be filled as needed. If a slot was opened, someone would be hired into it. If no slots were open, no one would be hired to cause others to be pushed out.

The problem is how to schedule. Unlike most jobs where everyone works set hours, the airline world deals with par and sub par schedules and all must be divided in some equitable way. After all, someone has to sit reserve. Seniority is logical in this sense, but is there another way? Food for thought anyways.