Is there a reason this ship has to be a ring? I thought the point of a hyperspace ring was to take something else into hyperspace, that could not go on its own, like Obi-Wan’s fighter in Attack of the Clones. But from what they are saying, the ring is going on its own, so, why? Why not strap all engines they salvaged onto a regular ship?
Yes, the purpose of a hyperspace ring is to connect to a smaller ship and haul it faster than it can go on its own. In the final episode of Rebels, Thrawn and Ezra were carried off far far away by those giant space whales we saw in Episode 2 (They carried away Thrawn's Star Destroyer) Actually if I remember correctly, he had a fleet, and they were all hauled away by lots and lots of giant space whales. Or maybe the whales destroyed some, and hauled the ship Ezra and Thrawn were on, or if all ships got carried away, they didn't necessarily get taken to the same place. In any case, to our characters, it's ambiguous as to whether Ezra is dead, and whether Thrawn is dead, and if alive, where they are.
Presumably, Thrawn at least survived and his ship(s?) is either too damaged or too slow to return without help. So instead of going to get him personally in a super-fast ship that they build, his allies here have apparently chosen to build a ring they can haul his ship back here to take on the Republic. Or maybe the ring is supposed to make multiple trips and haul back his entire fleet? I suppose Morgan is in communication with Thrawn somehow and this is what he's asked for.
