If Supernatural had been on HBO, the episode In the Beginning (4.03) would've had a different timeline. It would take place in 1982. John and Mary were already married and Dean would be alive. (Yes, there would be an awkward moment of him seeing/meeting himself as a kid.) Mary is out of the game, but of course we know she continued hunting the occasional case (Celebrating the Life of Asa Fox 12.06). So when she finds out that her friend is in the crosshairs of a demon she still goes to help. Azazel kills Samuel, Deanna and John, but the price to bring John back is more than a kiss. Mary sleeps with Azazel while he's possessing her dead dad, and he fathers Sam, which is why he has demon blood in him and demonic powers. Sam's psychic abilities would manifest similarly to Jesse's since he is the only other example of a demon/human offspring we have. There would still be other "special" kids out there who still have certain strengths and different powers, but Sam would be stronger because he is also a vessel. Mary would start to suspect something after Sam's birth, so Azazel would return to kill her shortly after and thus set in motion John's quest for revenge.
