It will be revealed there is only one Elidibus - the one we're dealing with is both the "heart of Zodiark" and the original from the Final Days. Venat mentions before becoming the "heart of Hydaelyn" that she would not vanish from the world and retain a form of her choosing; if that's the case it's entirely plausible Elidibus simply chose to keep his current form, and being Zodiark's "heart" just means he is in direct communion with the primal.

If the Crystal Tower series is a requirement for doing 5.3, Source G'raha is going to return to the stage in lieu of Crystal Exarch G'raha, since the latter is confined to the First. Some sort of memory transference may take place so we don't have to explain everything to him.

All the Scions will return to the Source safe and sound. Thancred and Urianger's departure from the Eden raids post-Refulgence suggests they will return, being the game's iconic hero protagonist there's no way they'd leave Y'shtola to rot on the First, and Alphinaud and Alisae are the story's real protagonists (or they were before Shadowbringers).

We know the Sapphire Weapon is more than likely to be the next Weapon trial, and I concur that van Hydrus will likely be the combat data loaded into it.

The YoRHa raid will be based on the carnival area from Automata, featuring the opera singer Simone as a / the final boss. Stay away from the crucified gynoids, folks!

(And don't worry about being bored; everyone is. I finished VII:R in about four days, overcame my disdain for EX trials to beat Memoria Misera for the dye-enabled AF gear, and whenever I suggest a time for my D&D group to meet up again I just get rebuked as being overly ambitious and told it's going to be months still... even though we've not been hit very hard locally... and it's already been 3 months since we last met...)