The kraken idea would still be more feasible if flooding flooded the whole field. I personally feel that one of the main problems with the current flooding is that you need seven creatures out before it will have any impact. In most cases, seven creatures is more than enough to win, so a person fighting against a flooding usually doesn't need to bother with it. In fact, I think it would be rather difficult to maintain that many creatures, outside of massive creature spam decks, due to all the cc that the opponent might have. I think by the time you would manage to play the kraken underwater, someone's probably going to win soon anyway.