They are unlikely to split the versions of the game into a last gen current gen as that means you double your development and testing as your now supporting two seperate games and need seperate teams to support it. Also you need a seperate code Base and project management for the releases. It's not going to happen if it did then they would most likely stop support for last gen all together to make it viable which would piss a lot of people off more than next gen asking for more vault.