I suggest that there be a frontlines map on the first. We need the first to get PVP representation. Shadowbringers was amazing.
My idea is that there would be three teams you would randomly be put on.
Team one would be the Warriors of Light. Team two would be the Warriors of Darkness, and Team three would be the Warriors of Dawn (yes, dawn is a thing).
Each corner of the map would be themed after a different location on the first. Light would be the Crystarium, and would have a lakeland theme. Darkness would be Eulmore, and would have a Kholusia theme. Dawn would have an Il Mheg theme with its Voebertian castle in the background.
In each corner the players would be summoned like the heroes were for the last dungeon in Shadowbringers, so the goal would be to overwhelm the opponents via summoning from other shards. It would play into this by having mechanics that involve summoning divine powers, and other Ascian related shenanigans. Would be a good way to memorialize these things, but make a fresh Frontlines mode that feels out of this world.