A waaaaaaaaayward random SPN thought
What if Sam *is* Lucifer's Trap now? A walking, talking, breathing and hunting one. Not the posessed pit-returnee, or the 'Devil's Vessel', per se, as he used to be. But what if having conquered Lucifer within enough to make the final leap, Sam somehow became the actual 'metaphysical' trap (and/or automatically reestablished the set of seals it would take to brake in order to ever free Lucifer again; 'the power of the human soul' - anyone?), thus making the previous 'downstairs' venue of Lucifer's custody redundant in the grand scheme of things. Hence - Sam's prompt and seemingly inexplicable 'resurrection'.
The energy and resolve it ought to take to keep the Devil trapped/incapacitated (whatever the original idea was back in the days of yore) might've been instrumental to Sam's obvious 'disconnection' from his own humanity as established in s6 so far. Incidentally that could've been the core of his reasoning behind not contacting Dean for that year, or being that distant/uncaring now - for Dean is *the* connection to Sam's very humanity. Hence, might I hypothesize, is the step to brake the first seal all over again (were the 'seal' to be the vulnerability of Sam's own soul, for instance), as viewed by Sam.
That is not in the very least to say Sam necessarily has to be the 'Devil's container' still, to be the way he is through s6 so far (Lucifer or no Lucifer - the guy had got gallons of demon blood coursing through his system alongside some major helping of residual adrenaline from having *been* literally the Devil incarnate, that *had* to pay off in some way) just entertaining a very random idea very late at night here.