So the NMB has been asked to decide between what appears to be two incompatible decisions. Either to issue a single carrier status determination as requested by APA, or allow the MB arbitration process to begin by providing a list of arbitrators as requested by USAPA. They can't do both, since doing the former renders the latter unnecessary.
On April 11 the NMB provided USAPA with exactly such a list of arbitrators, as requested. So they have already made a decision.
My uneducated guess is that the NMB, despite having no statutory constraints from doing so, will withhold single carrier certification until the MB injunction litigation is settled, or a negotiated settlement is reached between USAPA and APA.
But hey, I also thought UAL was a done deal.