The battle islands should function like the caves from Core Combat

[capiqu]

Even if mods or any kind of benefits are not attached to the capture of Nexus just the fact that you can use the rotating geo/warps to move into other continents is reason enough to have . They could serve as back doors to other continents.
Each cont with 2 geo/warps that could be located south to north or east to west of each other. That would be 8 geo/warps on Indar,Esamir,Amerish and Hossin. With 2 warpgates on Nexus each one connecting to 1 cont that would mean that Geo/warps will rotate every 6 hours.