New spoilers are popping that before the end of the season, Jensen Ackles is going to (finally) play someone different, and hints are that it's coming in the season finale, which suggests it's going to be a game-changer.
Prediction: they're *finally* going to spring Michael from the cage, only to find that Adam's body has disintegrated from its time down there (since unlike a "true" vessel it's not really strong enough to withstand prolonged possession anyway), meaning he'll need a new vessel...meaning Dean will finally say "yes" (eight years late). This in turn will be necessary because by then Lucifer will have regained his strength and it'll take the combined might of Gabriel and Michael to take him down.
Prediction: they're *finally* going to spring Michael from the cage, only to find that Adam's body has disintegrated from its time down there (since unlike a "true" vessel it's not really strong enough to withstand prolonged possession anyway), meaning he'll need a new vessel...meaning Dean will finally say "yes" (eight years late). This in turn will be necessary because by then Lucifer will have regained his strength and it'll take the combined might of Gabriel and Michael to take him down.