My guess is that 5.3 won't feature any of the Weapons as a Trial. Traditionally, we have a Story Trial in 5.3, and with it being said to be the climax of the Shadowbringers story I don't think it would be a Weapon that hardly featured in the main Scenario. (Suspecting 'Ardbert' instead.)
They already said Sapphire is next, yes... but my guess is that in good old FF VII Tradition, Sapphire is dealt with via cutscene, maybe Solo Duty, leaving Emerald and Diamond as proper Trials.
