This arbitration was simply a step in a internal union policy, it was not legislatively required by law, nor was it by court order, and unlike union/company arbitration, is not governed by the RLA.
It was simply part of a policy of a union that was replaced, and thus the policies were replaced.
There was nothing legally required about it and only had meaning as condition of membership. No different than being in a country club, being unsatisfied with the benefit of membership and taking your money elsewhere.
USAPA still has obligation as any union to its member but as it says in the ruling, an obligation to both East and West. When and if there is a lawsuit down the road, it will be judged on its own merit and only as it relates to finding an acceptable solution to all of its members. Unions are given a latitude to operate within a "wide range of reasonableness" in creating and administering polices. Longevity based integrations have never been overturned in a DFR case. So, it is likely that USAPA with a DOH policy + the 10 year conditions and restrictions proposed protecting all the West Captain jobs and rights to upgrade into them out of seniority and immediate access to East flying by DOH will likely be found within a "wide range of reasonableness."