I'm sure CorporalCaptain is referring to the popular fan theory that Coulson will be resurrected as the Vision rumours that have surfaced since the "Avengers", unless there are new rumours that I'm not aware of regarding how Coulson could return. Revealing that Coulson is alive would defeat the purpose of his death being the catalyst for uniting the team. Joss would not have done that. Coulson's death kind of reminded me of Wash's from "Serenity".
The Vision theory, what Christopher
said about the comic/SF staple, but also—let's face it—Coulson seems pretty popular. There's nothing like brining back popular
characters to really create a swell of enthusiasm.
I'm puzzled with your assessment that "Joss would not have done that." He and Penn already had Fury lie about the card to bring the team together; what's one more lie? The whole point of that scene
of the reveal of the lie is actually undermined if you just assume
that Fury's telling the truth.