Looks like Sigmascape will be FFVI-themed. I guess the last one will be VII or VIII-themed, whichever one has Omega Weapon (both I think?). I expect Omega Prime to be the final boss. I also expect to see Sephiroth as a boss at some point, but it wouldn't make sense for Kefka to be the final boss of this tier and Sephiroth not to be the final boss in the VII tier. Who knows, maybe they even deviate a bit from the pattern we had so far.