hypothetically if there was going to be sequel 2-3 years from now. i think it would be cool if we discovered there were several arcs all across the globe. some of them under water, in the air, in the arctic, etc.
these other arc's decide to invade brink's arc to steal their resources and the security and resistance form an alliance to fight the invasion. there's the same basic struggle with new enemies, new weapons, environments and missions types.
But the resistance would have left the ark, and having other arks would be highly unlikly, the ark was one of a kind, an technolgical wonder, self sustaining floatibg man made island, i doubt there are others around, unless other world nations built their own, but they would likley be diffrent, and if there are others built in america, im sure they would be able to contact eachother, but no other arks were mentioned , but it may be mentioned in the game later on.
What i was thinking is there won't be a brink 2, probably a non direct sequel like bioshock: infinite. It does not follow the bioshock story but it mantains many gameplay elements, such as plasmids, which are now called vigors (or something of the sort) the same cab be done with brink, keep the SMART system, the classes, etc, and put it in a diffrent story with a diffrent setting and add change a few things around, then BAM! Brink sequel.