Another Suggestion to these "Summons" could be like Odin/Behemoth Fates.

The uber strong ones come once every 36-72 hours. Everyone must Zerg them to finish them off or its a wipe.

Some of the others should be from Hunts meeting certain criteria.

Battle ships aren't a bad idea. Like fighting a boss like Leviathan on a battle ship but

What be awesome is an open world afterwards where more areas than we currently have to continue the story line. (Expansion)

Also maybe some Battle Arenas? Where you have certain levels from Light Party, to Alliance size groups. Fighting from 3-8 set of monsters depending on difficulty and then going to the "Primals" area.

Underworld needs to be added later. Fitting for Anima and Exodus.